It should have created a dump file. It sounds like gacutil crashed, and the dump file would have why. Although if you already clicked "Don't Send" or "Send" then the file would have been cleaned up.
If you get it again, do the click here link and find out where the dump files are, copy them to a safe location, and give me a shout (foyc at cornet design dot com). I'll be happy to dig into them to see what the heck went on (or you can do it with windbg+sos).