The issue dates back a while, but may still be relevant to people using Management Reporter. A client, unbeknown to me, decided to move Management Reporter to a new server; they'd been having HDD capacity problems on the existing SQL Server.
They'd migrated the databases and installed the services, correctly configuring the Legacy Connector, but were receiving an error:
The problem is that there are a few tasks which need to be undertaken when moving Management Reporter to a new server, including an encryption key which needs to be set. These are covered in this Microsoft Support article which includes, amongst other things, a script to run.