Not backing up computers?

I checked teh event viewer log , and see the following -

Backup job 113 on UNKILOSERVER did not succeed.  Reason: ClientVssInsufficientSpace, System.String

The drive on the client PC is a SSD drive. I believe it is NTFS (it is a relatively, less than 6 months old, new Win 7, 64 bit install).

Does that help? Thanks for your help…