The VSS writer error that seems to cause the most trouble for people is missing SqlServerWriter from the results list when using the VSSAdmin List Writers command. There are two main causes for this error.
The most common issue is a permissions problem. The service account (usually NT Authority/system) must have sysadmin privileges on SQL Server.
The other thing that can cause problems is leading or trailing spaces in a database name. To see if this is the problem, try running the following query:
Select '#'+name+'#' from sys.database
If any results are returned, then the database appearing in the results has a space in the name.
This was first published in April 2013