It is likely you are hitting this bug that I recently fixed:
Can you check your eclipse error log and see if the null pointer exception is there (as reported in the bug). (Get the error log via menu 'Windows >> Show View >> Error Log'.
If this is the bug you are hitting then you can find a possible workaround in the bug report. Also, you can update the Grails tooling from the nightly update site to get the bugfix.
Let me know if you need more help with any of that.
Kris De Volder -- SpringSource