If the credentials are not anymore in the Credentials location, you cannot do anything about it but if you have a backup of the database.
If this is the case, you need to:
1. backup your recent DB 2. restore temporarily the backed up DB 3. use the JMX-console to export the domain scope document (I think it's documented in the manual how to do that) 4. restore back to the most recent DB 5. import the Domain Scope Document and everything should like it was in the backup DB.
But be careful, that you might lose the difference between the moment you did the backup (I mean the old backup) and the current time.
Of course, like every recommendation, don't go eyes shut into the solution but test it first.
This forum remind me the time when I was in the support (sob!) ;-p