If other users have the common email queue open for sending you will see this message. It is possible that after a power failure or not shutting down Windows or Schedule it correctly that the email queue could be locked open. If you are sure the user has closed the email queue you can reset this lock.
You can see the user and computer that has the event open under the Activity tab in the event and filter for the action Email_Sending.
Method 1:
Get the same user that had the queue open previously to reopen the queue on the original computer. Then close the queue to remove the lock.
Method 2:
As an Administrator, from the Tools menu, select Activity Log,
In the 'Filter by action', choose 'Email_Sending',
Press the button 'Clear Selected' to remove the user lock entry.
Last updated, 27 January 2013, 15:42