Another possibility is a mismatch between the collection ID in the catalog and the collection ID in the collection table. OAM checks for this condition when the OAM address space is started. Check your syslog during OAM address space initialization for message CBR9030I, or any other messages that might indicate a problem with the catalog.

LISTCAT ENTRIES('collection_name') ALL

Verify that the DIRECTORYTOKEN matches the Object storage group name for qualifier HLQ on the ISMF storage group definition panel. Be sure to use ACTIVE as the SCDS name when listing Object storage group information. The Object storage group name must also match storage group name (ODCLSGNM) in the collection table.