Ensure that the password for the ERM service account is still valid. Attempt to verify the ERM service account from the ERM Mailbox Browser by clicking Edit -> Product Configuration -> Service Account tab -> Verify. Correct any pop up errors. Additionally, there may be errors in the ERM_RCS.Mdb file located typically in \Program Files\Simpler-Webb\Exchange Resource Manager\Data. You can either email the database compressed in a zip file to an ERM support tech to be corrected or:
Edit the database using Microsoft Access.
1. Open the database in Access
2. Sort by index smallest to largest
3. Locate the column labelled SZSignature. The first record (index 1) should be blank as this is the ERM Base Configuration record. All additional records in this column should display Alphabetic values such as DDAKLMMIOMJFAAMKDOKICCEPNBGOCCDPIILFLEDGALNBKEJNJPJIPPBICDBAPONN
4. Any blank record can be safely deleted by selecting the whole row on the left most column and hitting delete on the keyboard or right-click delete. In databases with a large number of resources there may be many records with blank SzSignature fields. All can be safely deleted except the ERM Base Configuration Record.
5. Compact and Repair the database to shrink the size. Your final database should be 300-600kb, generally.
6. If the editing was done in a location different than your ERM server, just copy the database over the top of the existing database, replacing the original.
7. Unmanage and remanage any resource that was failing to respond. Send a test invitation to the resource. It should start responding.