See the IBM® Tivoli® Storage Manager error logs for additional information.

One of the VSS writers is in an invalid or unexpected state. Try the command "vssadmin list writers" and check the state of VSS writers. Writers must be in STABLE state before IBM Tivoli Storage Manager can continue with VSS operations. Some of the writers can recover automatically from minor errors. In most cases, restarting a writer solves the problem. The easiest way to restart writers is to restart the operating system. It is possible to restart the specific service that implements a VSS writer, but it is difficult to determine which service to restart.