V7 error "Your start up disk doesn't have enough space"

Had this strange crash today running V7. I got a message from the finder that there wasn't sufficient space on the start up disk and that I should close one of the applications that I wasn't using and it presented a list of the open applications. C1 was highlighted in red as not responding and the only option was to force quit. It's a bit frustrating because actually I hadn't been doing anything with C1 v7. I also checked and I have over 100gb of free space on the hard drive and I am running 24gb RAM on this machine. Hmmm... I forced C1 to quit and restarted. What could C1 be doing with the start up disk?