Problem: Symantec backup exec 2012 run a backup job and failed with vss writer error message. Login Exchange server => Open CMD => vssadmin list writers => saw Microsoft Exchange VSS writer in retryable error stage. This need to be "No error" and State: Stable in order for backup jobs tow ork.
When contact Symantec they said to restart the exchange server, yes it will temporarily solve it. BUT IT IS NOT THE ANSWER!!! and if you contact Microsoft they will point finger back and forth.
Solution: With many Google searches below are the possible links to fix your VSS problems without Exchange reboot but here is the solution that solved mines.
1) Make sure you ONLY have 1 exchange job running, another exchange job running will cause the VSS error.
2) Restart the Exchange Replication Service
Here are list of links that may solve your VSS error if the top solution didn't do it for you.