error Google GWT

[Nadrahalshitwi]

I got this error when I install WGT
Errors occurred during the build.
Errors running builder 'GWT Project Validator' on project 'logicaldoc-gui'.
org.eclipse.jdt.internal.core.JavaProject.computePackageFragmentRoots([Lorg/eclipse/jdt/core/IClasspathEntry;ZLjava/util/Map;)[Lorg/eclipse/jdt/core/IPackageFragmentRoot;
best regards