The shadow copies of volume C: were aborted because the shadow copy storage could not grow due to a user imposed limit.
We got this error on a 64-bit Vista machine every night at around 8PM. The error didn't seem to cause any problems, since the system restore feature appeared to work correctly.
Still, investigating this error led us to the "vssadmin" tool that lets you adjust the size of the shadow copy storage.
Run "vssadmin list shadowstorage" to see the currently allocated storage, and run "vssadmin resize shadowstorage" (with the appropriate options) to increase the space for shadow storage.
For example, you could run:
vssadmin Resize ShadowStorage /For=C: /On=: /MaxSize=10GB