Symptom: Rollup fails with 'SQL Server does not exist or credentials are not valid' after creating successful database links.
Cause: The rollup core has to be able to resolve the database name it is rolling up via the name in the registry on the core server. If the core server lists the DB by hostname and the core can only hit is by FQDN for example, then the rollup will fail.
Resolution: Change the Server name field in the registry on the CORE server under HKLM\Software\LANDesk\ManagementSuite\Core\Connections\Local to a name or address that the ROLLUP core can resolve for the database. This key is used to build the SQL Connection String that the Rollup uses to talk to the database.