HP Data Protector A.06.11 Integration Manual page 209

Problem
Creation of an RSG fails when an RSG for the same storage group already exists
When you start a restore of the Microsoft Exchange Server 2007 writer with the
option Restore to a non-Exchange location and create RSG, the
following error is displayed:
[Major]
Application specific function 'PostRestoreEndExt' failed with error:
'The mailbox database that you specified is already associated with
a recovery mailbox database.
This error appears if an RSG for a storage group or mailbox database you restore
is already created on some other system.
Action
Since only one RSG can exist for the same storage group and since Data Protector
can only delete an RSG that exists on the target restore location, you need to manually
delete the RSG on the other system and restart the restore.
Integration guide for Microsoft applications 209