D [04/Mar/2010:17:00:15 +0100] [Job 4939] cat: write error: No space left on device
So it seems that CUPS is not able to create the temporary files needed to process your print jobs due to lack of disk space. CUPS puts these files into /var/spool/cups and /var/spool/cups/tmp.
Your error_log shows
D [04/Mar/ 2010:17: 00:15 +0100] [Job 4939] cat: write error: No space left on device
So it seems that CUPS is not able to create the temporary files needed to process your print jobs due to lack of disk space. CUPS puts these files into /var/spool/cups and /var/spool/ cups/tmp.