Every once in a while a Grails application will behave completely weirdly throwing out completely unrelated errors when you try to do add or edit some domain objects. I found that deleting the .grails directly and then rebuilding the application clears out that problem. On Windows, the directory is located at C:\\Documents and Settings\\userid. The only impact this will have is that any plugin that the application may be using will be reinstalled by the Grails runtime system (possibly through Maven).