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$2.run(ProjectsRootNode.java:766)
        at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:576)
        at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:1013)