Error when I delete user account and try to save it in the deleted users folder

I am trying to delete a user account and save it as a dmg file in the deleted users folder. The process runs for 20-30 minutes, then returns the error message "mac unable to back up users home file." There is no guidance in this message as to what went wrong. I tried rebooting, deleting files from the user account, emptying trash. The user account is about 4.5gb in size, mostly media files (music, flv, swf, mov, wav, jpg, mp3, etc.). I can copy these files and save them separately, but I really do want to preserve the configuration details for this account. Any ideas? Thanks. Steven B.