mudmask, just an educated guess - I had the same problem intermittently for a long time because I used to keep records and plans in Word in the root folder. I found that if I pressed return it would cancel the save when it hung... When I analysed the failure message there was a snippet of the windows backup file (the abbreviated one with $ symbols). I moved my files and there was no longer a problem.
Another thought... If you save your backups to the same folder as the primary c2 capx/caproj then your backups will contain your backups, will contain your backups... Make sure you're not causing it to hang on memory...