Sorry for my former post, I should searched other posts to find the answer. The problem was indeed solved here https://groups.google.com/forum/#!searchin/google-web-toolkit/WebAppCreator$20failed/google-web-toolkit/RjmfYcmvvXE/jqbeQEol5EUJ , with the link to https://code.google.com/p/google-web-toolkit/issues/detail?id=5586.
This workaround - delete external classpath - also solved my problem. -- You received this message because you are subscribed to the Google Groups "GWT Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/google-web-toolkit. For more options, visit https://groups.google.com/d/optout.
