Users are unable to update tickets because of errors AHD04603 (Unable to checkout) and AHD03026 (Checked out by another user)
The solution requires tuning the ExclLockSeconds parameter in the web.cfg file. The default is 120 (seconds), which means users get an exclusive lock on a ticket for 120 seconds after pressing the Edit button. Reducing this value gives users less time to edit the ticket, but will also reduce the chance that other users are unable to check out the ticket.
In addition, the Timeout parameter in web.cfg may be tuned. The default is 60 (minutes), which means that user sessions will be cancelled after 60 minutes idle time. All resources are then released, which includes any exclusive locks on tickets that the user was editing. Reducing this value may also increase the likelihood that tickets are available for other users to check out.
In any event, be sure that ExclLockSeconds is less than Timeout, keeping in mind that ExclLockSeconds in in seconds and Timeout is in minutes.