PROBLEM
The WSUS Server stop synchronize with the slaves servers, and you have a similar error in your WSUS log file
SqlException: The specified revision could not be found.
at Microsoft.UpdateServices.DatabaseAccess.DBConnection.DrainObsoleteConnections(SqlException e)
at Microsoft.UpdateServices.DatabaseAccess.DBConnection.ExecuteReader()
at Microsoft.UpdateServices.Internal.SingleResultSetSPHandler.ExecuteStoredProcedure(DBConnection connection)
at Microsoft.UpdateServices.Internal.GenericDataAccess.ExecuteSP(String spName, DBParameterCollection args, IExecuteSPHandler handler, Int32 queryTimeoutInSeconds)
at Microsoft.UpdateServices.Internal.GenericDataAccess.ExecuteSP(String spName, DBParameterCollection args, IExecuteSPHandler handler)
at Microsoft.UpdateServices.Internal.DatabaseAccess.CommonDataAccess.ExecuteSPSingleResultSet(String spName, DBParameterCollection args, Type resultType, Int32 queryTimeoutInSeconds)
at Microsoft.UpdateServices.Internal.DatabaseAccess.CommonDataAccess.ExecuteSPSingleResultSet(String spName, DBParameterCollection args, Type resultType)
at Microsoft.UpdateServices.Internal.DatabaseAccess.Admin
CAUSE
Microsoft BUG
SOLUTION
Apply the WSUS 3.0 SP1