I know ntozier won't appreciate me bringing up a "zombie" thread, but it comes up on Google search regardless of whether it's old or not – as long as it's relevant, which to me it was.
Here's what fixed it for me:
- Go to https://example.com/scp/staff.php
- In the list, click the name of the agent who can't act on a ticket
- Once on the agent editing page, go to the Access tab
- Make sure the agent has access to the problematic ticket's department; if multiple departments are required – add them all under Extended Access
The problem happened when I created a new sub-department under my main department and moved my tickets into that new sub-department. It turns out that by default existing users, including the admins, won't have access to any new departments, and furthermore, when tickets that they currently have access to are moved, they actually lose their permissions.
My osTicket version is v1.12.5-88