When a Quarantine is in Inactive mode, attempts to modify the contents of that quarantine by releasing, deleting, or otherwise taking action on messages will fail silently in the UI but an error will be logged to the BrightmailLog.log:
ERROR - Unable to release spam message(s): quarantine is in INACTIVE mode
Version: 10.9.0
The Control Center host has had its IP changed in the past and is now attempting to connect to the old IP to activate the quarantine.
Please note that this a separate issues from the inactive quarrantine in Messaging Gateway 10.8.0 which can be addressed by applying the 10.8.0 patch or updating to 10.8.1.
For Messaging Gateway 10.9.0 a support case will need to be opened to address the IP configuration issue directly.