A Provider staff member cannot edit tickets in the PBA Provider Control Panel at Operation Director > Support Manager > Queues > select a queue > select a ticket. After pressing Edit > Update the 'Access Denied' error message is displayed.
It is not possible to edit an existing ticket with empty 'Subscription' field due to the defect PBA-37486.
The problem is fixed since the PBA 5.4.9, consider to upgrade to this version to resolve the issue.
In the meantime, it is possible to assign subscription to the problem ticket if there is an existing subscription belonging to the Requester of the ticket.