This is a simple one.
Mysteriously the auto-compile for controllers (but not views) in my grails v1.1.1 application stopped working. It worked fine for the other engineers on this project so I did the normal poking around. Surprisingly I could not find anything on Google.
To fix this problem, try deleting your ~/.grails directory. You'll need to download all of your plugins again, but autocompile will work once again.