I have openfire 4.0.1 working with ofmeet 0.3.1, when I updated ofmeet to 0.3.8 obtained this error:
2016.02.03 19:26:58 org.jivesoftware.openfire.container.PluginManager - Error loading plugin: /usr/share/openfire/plugins/ofmeet java.lang.UnsupportedClassVersionError: org/jivesoftware/openfire/plugin/ofmeet/OfMeetPlugin : Unsupported major.minor version 52.0 at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClass(ClassLoader.java:800) at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142) at java.net.URLClassLoader.defineClass(URLClassLoader.java:449) at java.net.URLClassLoader.access$100(URLClassLoader.java:71) at java.net.URLClassLoader$1.run(URLClassLoader.java:361) at java.net.URLClassLoader$1.run(URLClassLoader.java:355) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:354) at java.lang.ClassLoader.loadClass(ClassLoader.java:425) at java.lang.ClassLoader.loadClass(ClassLoader.java:358) at org.jivesoftware.openfire.container.PluginManager.loadPlugin(PluginManager.java:379) at org.jivesoftware.openfire.container.PluginManager.access$300(PluginManager.java:68) at org.jivesoftware.openfire.container.PluginManager$PluginMonitor.run(PluginManager.java:1037) at org.jivesoftware.openfire.container.PluginManager.installPlugin(PluginManager.java:176) at org.jivesoftware.openfire.update.UpdateManager.downloadPlugin(UpdateManager.java:286) at org.jivesoftware.openfire.update.PluginDownloadManager.downloadPlugin(PluginDownloadManager.java:45) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:606) at uk.ltd.getahead.dwr.impl.ExecuteQuery.execute(ExecuteQuery.java:248) at uk.ltd.getahead.dwr.impl.DefaultExecProcessor.handle(DefaultExecProcessor.java:48) at uk.ltd.getahead.dwr.impl.DefaultProcessor.handle(DefaultProcessor.java:81) at uk.ltd.getahead.dwr.AbstractDWRServlet.doPost(AbstractDWRServlet.java:162) at javax.servlet.http.HttpServlet.service(HttpServlet.java:707) at javax.servlet.http.HttpServlet.service(HttpServlet.java:790) at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:812) at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1669) at org.jivesoftware.admin.AuthCheckFilter.doFilter(AuthCheckFilter.java:162) at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1652) at com.opensymphony.module.sitemesh.filter.PageFilter.parsePage(PageFilter.java:118) at com.opensymphony.module.sitemesh.filter.PageFilter.doFilter(PageFilter.java:52) at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1652) at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:585) at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:143) at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:577) at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:223) at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1127) at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:515) at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:185) at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1061) at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:141) at org.eclipse.jetty.server.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:215) at org.eclipse.jetty.server.handler.HandlerCollection.handle(HandlerCollection.java:110) at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:97) at org.eclipse.jetty.server.Server.handle(Server.java:499) at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:311) at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:257) at org.eclipse.jetty.io.AbstractConnection$2.run(AbstractConnection.java:544) at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:635) at org.eclipse.jetty.util.thread.QueuedThreadPool$3.run(QueuedThreadPool.java:555) at java.lang.Thread.run(Thread.java:745) 2016.02.03 19:27:12 org.jivesoftware.openfire.container.PluginManager - Error loading plugin: /usr/share/openfire/plugins/ofmeet java.lang.UnsupportedClassVersionError: org/jivesoftware/openfire/plugin/ofmeet/OfMeetPlugin : Unsupported major.minor version 52.0 at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClass(ClassLoader.java:800) at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142) at java.net.URLClassLoader.defineClass(URLClassLoader.java:449) at java.net.URLClassLoader.access$100(URLClassLoader.java:71) at java.net.URLClassLoader$1.run(URLClassLoader.java:361) at java.net.URLClassLoader$1.run(URLClassLoader.java:355) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:354) at java.lang.ClassLoader.loadClass(ClassLoader.java:425) at java.lang.ClassLoader.loadClass(ClassLoader.java:358) at org.jivesoftware.openfire.container.PluginManager.loadPlugin(PluginManager.java:379) at org.jivesoftware.openfire.container.PluginManager.access$300(PluginManager.java:68) at org.jivesoftware.openfire.container.PluginManager$PluginMonitor.run(PluginManager.java:1037) at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471) at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:304) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:178) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615) at java.lang.Thread.run(Thread.java:745) 2016.02.03 19:27:32 org.jivesoftware.openfire.container.PluginManager - Error loading plugin: /usr/share/openfire/plugins/ofmeet java.lang.UnsupportedClassVersionError: org/jivesoftware/openfire/plugin/ofmeet/OfMeetPlugin : Unsupported major.minor version 52.0 at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClass(ClassLoader.java:800) at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142) at java.net.URLClassLoader.defineClass(URLClassLoader.java:449) at java.net.URLClassLoader.access$100(URLClassLoader.java:71) at java.net.URLClassLoader$1.run(URLClassLoader.java:361) at java.net.URLClassLoader$1.run(URLClassLoader.java:355) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:354) at java.lang.ClassLoader.loadClass(ClassLoader.java:425) at java.lang.ClassLoader.loadClass(ClassLoader.java:358) at org.jivesoftware.openfire.container.PluginManager.loadPlugin(PluginManager.java:379) at org.jivesoftware.openfire.container.PluginManager.access$300(PluginManager.java:68) at org.jivesoftware.openfire.container.PluginManager$PluginMonitor.run(PluginManager.java:1037) at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471) at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:304) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:178) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615) at java.lang.Thread.run(Thread.java:745) 2016.02.03 19:27:52 org.jivesoftware.openfire.container.PluginManager - Error loading plugin: /usr/share/openfire/plugins/ofmeet java.lang.UnsupportedClassVersionError: org/jivesoftware/openfire/plugin/ofmeet/OfMeetPlugin : Unsupported major.minor version 52.0 at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClass(ClassLoader.java:800) at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142) at java.net.URLClassLoader.defineClass(URLClassLoader.java:449) at java.net.URLClassLoader.access$100(URLClassLoader.java:71) at java.net.URLClassLoader$1.run(URLClassLoader.java:361) at java.net.URLClassLoader$1.run(URLClassLoader.java:355) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:354) at java.lang.ClassLoader.loadClass(ClassLoader.java:425) at java.lang.ClassLoader.loadClass(ClassLoader.java:358) at org.jivesoftware.openfire.container.PluginManager.loadPlugin(PluginManager.java:379) at org.jivesoftware.openfire.container.PluginManager.access$300(PluginManager.java:68) at org.jivesoftware.openfire.container.PluginManager$PluginMonitor.run(PluginManager.java:1037) at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471) at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:304) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:178) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615) at java.lang.Thread.run(Thread.java:745) 2016.02.03 19:28:12 org.jivesoftware.openfire.container.PluginManager - Error loading plugin: /usr/share/openfire/plugins/ofmeet java.lang.UnsupportedClassVersionError: org/jivesoftware/openfire/plugin/ofmeet/OfMeetPlugin : Unsupported major.minor version 52.0 at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClass(ClassLoader.java:800) at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142) at java.net.URLClassLoader.defineClass(URLClassLoader.java:449) at java.net.URLClassLoader.access$100(URLClassLoader.java:71) at java.net.URLClassLoader$1.run(URLClassLoader.java:361) at java.net.URLClassLoader$1.run(URLClassLoader.java:355) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:354) at java.lang.ClassLoader.loadClass(ClassLoader.java:425) at java.lang.ClassLoader.loadClass(ClassLoader.java:358) at org.jivesoftware.openfire.container.PluginManager.loadPlugin(PluginManager.java:379) at org.jivesoftware.openfire.container.PluginManager.access$300(PluginManager.java:68) at org.jivesoftware.openfire.container.PluginManager$PluginMonitor.run(PluginManager.java:1037) at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471) at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:304) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:178) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615) at java.lang.Thread.run(Thread.java:745) 2016.02.03 19:28:32 org.jivesoftware.openfire.container.PluginManager - Error loading plugin: /usr/share/openfire/plugins/ofmeet java.lang.UnsupportedClassVersionError: org/jivesoftware/openfire/plugin/ofmeet/OfMeetPlugin : Unsupported major.minor version 52.0 at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClass(ClassLoader.java:800) at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142) at java.net.URLClassLoader.defineClass(URLClassLoader.java:449) at java.net.URLClassLoader.access$100(URLClassLoader.java:71) at java.net.URLClassLoader$1.run(URLClassLoader.java:361) at java.net.URLClassLoader$1.run(URLClassLoader.java:355) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:354) at java.lang.ClassLoader.loadClass(ClassLoader.java:425) at java.lang.ClassLoader.loadClass(ClassLoader.java:358) at org.jivesoftware.openfire.container.PluginManager.loadPlugin(PluginManager.java:379) at org.jivesoftware.openfire.container.PluginManager.access$300(PluginManager.java:68) at org.jivesoftware.openfire.container.PluginManager$PluginMonitor.run(PluginManager.java:1037) at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471) at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:304) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:178) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615) at java.lang.Thread.run(Thread.java:745) 2016.02.03 19:28:52 org.jivesoftware.openfire.container.PluginManager - Error loading plugin: /usr/share/openfire/plugins/ofmeet java.lang.UnsupportedClassVersionError: org/jivesoftware/openfire/plugin/ofmeet/OfMeetPlugin : Unsupported major.minor version 52.0 at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClass(ClassLoader.java:800) at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142) at java.net.URLClassLoader.defineClass(URLClassLoader.java:449) at java.net.URLClassLoader.access$100(URLClassLoader.java:71) at java.net.URLClassLoader$1.run(URLClassLoader.java:361) at java.net.URLClassLoader$1.run(URLClassLoader.java:355) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:354) at java.lang.ClassLoader.loadClass(ClassLoader.java:425) at java.lang.ClassLoader.loadClass(ClassLoader.java:358) at org.jivesoftware.openfire.container.PluginManager.loadPlugin(PluginManager.java:379) at org.jivesoftware.openfire.container.PluginManager.access$300(PluginManager.java:68) at org.jivesoftware.openfire.container.PluginManager$PluginMonitor.run(PluginManager.java:1037) at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471) at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:304) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:178) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615) at java.lang.Thread.run(Thread.java:745)