BusinessObjects Enterprise or Edge? Crystal Reports Server? Crystal Enterprise? What are you using to schedule your reports? Which version?
Have you looked at the servers in the CMC to make sure everything is running correctly?
Crystal is a disk-hog and doesn't always clean up after itself very well so it eats up disk space. On your server, do a search for "~*.rpt". This is the filename format for Crystal temp files. Delete ALL of them that are not dated the current day.
How long has it been since youre server has been rebooted? Some versions have known memory leaks and you have to either stop all of the services and restart them on a regular basis or you have to reboot the server.
-Dell