java.lang.IllegalStateException: registerExternalRoots was already called before
        at org.netbeans.spi.project.support.ant.SourcesHelper.registerExternalRoots(SourcesHelper.java:513)
        at org.netbeans.modules.j2ee.earproject.EarSources$2.run(EarSources.java:93)
        at org.openide.util.Mutex.leaveImpl(Mutex.java:902)
        at org.openide.util.Mutex.leave(Mutex.java:835)
        at org.openide.util.Mutex.readAccess(Mutex.java:333)
        at org.openide.util.Mutex$1R.run(Mutex.java:1299)
        at org.netbeans.api.project.ProjectManager$2$1.run(ProjectManager.java:120)
        at org.openide.filesystems.EventControl.runAtomicAction(EventControl.java:120)
        at org.openide.filesystems.FileSystem.runAtomicAction(FileSystem.java:499)
        at org.openide.filesystems.FileUtil.runAtomicAction(FileUtil.java:167)
        at org.netbeans.api.project.ProjectManager$2.execute(ProjectManager.java:118)
        at org.openide.util.Mutex.doWrapperAccess(Mutex.java:1320)
        at org.openide.util.Mutex.readAccess(Mutex.java:275)
        at org.netbeans.modules.java.source.classpath.GlobalSourcePath.getLibsSources(GlobalSourcePath.java:518)
        at org.netbeans.modules.java.source.classpath.GlobalSourcePath.getSources(GlobalSourcePath.java:384)
        at org.netbeans.modules.java.source.classpath.GlobalSourcePath.createResources(GlobalSourcePath.java:275)
        at org.netbeans.modules.java.source.classpath.GlobalSourcePath.access$2200(GlobalSourcePath.java:95)
        at org.netbeans.modules.java.source.classpath.GlobalSourcePath$SourcePathImplementation.getResources(GlobalSourcePath.java:638)
        at org.netbeans.api.java.classpath.ClassPath.entries(ClassPath.java:296)
        at org.netbeans.modules.java.source.usages.RepositoryUpdater$CompileWorker$1.run(RepositoryUpdater.java:1304)
        at org.netbeans.modules.java.source.usages.RepositoryUpdater$CompileWorker$1.run(RepositoryUpdater.java:1252)
        at org.netbeans.modules.java.source.usages.ClassIndexManager.writeLock(ClassIndexManager.java:105)
        at org.netbeans.modules.java.source.usages.RepositoryUpdater$CompileWorker.run(RepositoryUpdater.java:1249)
        at org.netbeans.modules.java.source.usages.RepositoryUpdater$CompileWorker.run(RepositoryUpdater.java:1210)
        at org.netbeans.api.java.source.JavaSource$CompilationJob.run(JavaSource.java:1533)
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:441)
        at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
        at java.util.concurrent.FutureTask.run(FutureTask.java:138)
        at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:885)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:907)
        at java.lang.Thread.run(Thread.java:619)