-24974: ERR_XPSESSION - param session active 

Explanation:

If a parameter session is already active, you will not be able to start another session.

User Action:

Check the sequence of your DBM commands. If necessary, terminate an existing parameter session using param_commitsession or param_abortsession. Alternatively, you can also use the active parameter session to execute your command.

If the error occurs in Database Manager GUI and there is no way in which you can correct it, please contact Support.