java.lang.IllegalStateException: registerExternalRoots was already called
        at org.netbeans.spi.project.support.ant.SourcesHelper.addPrincipalSourceRoot(SourcesHelper.java:404)
        at org.netbeans.spi.project.support.ant.SourcesHelper.addPrincipalSourceRoot(SourcesHelper.java:365)
        at org.netbeans.modules.j2ee.earproject.EarSources.initSources(EarSources.java:92)
        at org.netbeans.modules.j2ee.earproject.EarSources.access$100(EarSources.java:60)
        at org.netbeans.modules.j2ee.earproject.EarSources$1.run(EarSources.java:81)
        at org.netbeans.modules.j2ee.earproject.EarSources$1.run(EarSources.java:78)
        at org.openide.util.Mutex.readAccess(Mutex.java:285)
        at org.netbeans.modules.j2ee.earproject.EarSources.getSourceGroups(EarSources.java:78)
        at org.netbeans.spi.project.support.LookupProviderSupport$SourcesImpl.getSourceGroups(LookupProviderSupport.java:279)
        at org.netbeans.modules.project.ui.ProjectsRootNode$BadgingNode.setProjectFiles(ProjectsRootNode.java:550)
        at org.netbeans.modules.project.ui.ProjectsRootNode$BadgingNode.setProjectFiles(ProjectsRootNode.java:469)
        at org.netbeans.modules.project.ui.ProjectsRootNode$BadgingNode$2.run(ProjectsRootNode.java:766)
Caused: org.openide.util.RequestProcessor$Item: task failed: java.lang.IllegalStateException: registerExternalRoots was already called
        at org.openide.util.RequestProcessor$Item.fillInStackTrace(RequestProcessor.java:853)
        at java.lang.Throwable.<init>(Throwable.java:181)
        at java.lang.Exception.<init>(Exception.java:29)
        at org.openide.util.RequestProcessor$Item.<init>(RequestProcessor.java:819)
        at org.openide.util.RequestProcessor$Task.schedule(RequestProcessor.java:629)
        at org.openide.util.RequestProcessor.post(RequestProcessor.java:295)
        at org.openide.util.RequestProcessor.post(RequestProcessor.java:266)
        at org.netbeans.modules.project.ui.ProjectsRootNode$BadgingNode.stateChanged(ProjectsRootNode.java:764)
        at org.openide.util.WeakListenerImpl$Change.stateChanged(WeakListenerImpl.java:321)
        at org.openide.util.ChangeSupport.fireChange(ChangeSupport.java:123)
        at org.openide.util.ChangeSupport.fireChange(ChangeSupport.java:109)
        at org.netbeans.spi.project.support.LookupProviderSupport$SourcesImpl.stateChanged(LookupProviderSupport.java:296)
        at org.openide.util.ChangeSupport.fireChange(ChangeSupport.java:123)
        at org.openide.util.ChangeSupport.fireChange(ChangeSupport.java:109)
        at org.netbeans.modules.j2ee.earproject.EarSources.fireChange(EarSources.java:113)
        at org.netbeans.modules.j2ee.earproject.EarSources.stateChanged(EarSources.java:120)
        at org.openide.util.ChangeSupport.fireChange(ChangeSupport.java:123)
        at org.openide.util.ChangeSupport.fireChange(ChangeSupport.java:109)
        at org.netbeans.spi.project.support.ant.SourcesHelper$SourcesImpl.maybeFireChange(SourcesHelper.java:828)
        at org.netbeans.spi.project.support.ant.SourcesHelper$SourcesImpl.fileDeleted(SourcesHelper.java:843)
        at org.openide.filesystems.FileUtil$Holder.fileDeleted(FileUtil.java:359)
        at org.openide.filesystems.FCLSupport$DispatchEventWrapper.dispatchEventImpl(FCLSupport.java:139)
        at org.openide.filesystems.FCLSupport$DispatchEventWrapper.dispatchEvent(FCLSupport.java:122)
        at org.openide.filesystems.FCLSupport.dispatchEvent(FCLSupport.java:99)
        at org.openide.filesystems.FileObject$ED.dispatch(FileObject.java:1014)
        at org.openide.filesystems.FileSystem$EventDispatcher.run(FileSystem.java:925)
        at org.openide.filesystems.EventControl.dispatchEvent(EventControl.java:77)
        at org.openide.filesystems.FileSystem.dispatchEvent(FileSystem.java:544)
        at org.openide.filesystems.FileObject.dispatchEvent(FileObject.java:469)
        at org.openide.filesystems.FileObject.fireFileDeletedEvent(FileObject.java:445)
        at org.netbeans.modules.masterfs.filebasedfs.fileobjects.BaseFileObj.fireFileDeletedEvent(BaseFileObj.java:532)
        at org.netbeans.modules.masterfs.filebasedfs.fileobjects.FolderObj.delete(FolderObj.java:329)
        at org.netbeans.modules.masterfs.filebasedfs.fileobjects.BaseFileObj$2.call(BaseFileObj.java:580)
        at org.netbeans.modules.masterfs.filebasedfs.fileobjects.BaseFileObj$2.call(BaseFileObj.java:575)
        at org.netbeans.modules.masterfs.filebasedfs.FileBasedFileSystem.runAsInconsistent(FileBasedFileSystem.java:112)
        at org.netbeans.modules.masterfs.filebasedfs.fileobjects.BaseFileObj.delete(BaseFileObj.java:588)
        at org.openide.filesystems.FileObject.delete(FileObject.java:359)
        at org.netbeans.modules.project.uiapi.DefaultProjectOperationsImplementation.performDelete(DefaultProjectOperationsImplementation.java:144)
        at org.netbeans.modules.project.uiapi.DefaultProjectOperationsImplementation.access$200(DefaultProjectOperationsImplementation.java:98)
        at org.netbeans.modules.project.uiapi.DefaultProjectOperationsImplementation$1.execute(DefaultProjectOperationsImplementation.java:203)
        at org.netbeans.modules.project.uiapi.DefaultProjectOperationsImplementation$6$1.run(DefaultProjectOperationsImplementation.java:655)
        at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:576)
        at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:1013)