IBM's documentation contains the following description of this error:
CTJTD3602E: The Change Manager is still processing. Wait and retry the discovery at a later time.
Explanation: The Change Manager is still running to process recent changes discovered. The discovery cannot be started until the Change Manager completes.
Operator Response: None.
Administrator Response: Allow time for the Change Manager to complete its processing before starting a discovery.
Programmer Response: None.
What we have found is that this condition can possibly occur for at least a couple of different reasons. The two situations we've found have been:
1. There was a deadlock on the database that we had to clear. A "little while" after we cleared the lock, we were able to successfully run a discovery again without receiving the error message.
2. The change manager partially ran, but didn't update the CHANGE_SERVER_STATUS table. Specifically, it left the value of the STATUS column set to 16 for the last discovery. To fix this, we had to run the following SQL:
update DB2TADDM.CHANGE_SERVER_STATUS set status = 17
This updates the STATUS column for all rows in the table. You could limit it with a WHERE clause, but in our case, it was valid as is.
We then needed to stop and restart TADDM, and the error message went away.