One of our clients has been receiving this error for every backup, on all 6 volumes, since 5/28/14. We had a technician work with SP Support, and they discovered the VSS Writers were in a failed state, so they went through the VSS KB article. This still has not fixed our problem.
Currently, that Tech is out sick, and did not happen to leave a SP Support Ticket # for us to reference, but each log has the following: