When a screen is associated with a transition, but no longer exists, the transition fails with the error:

"You don't have permission to transition this issue"

This is actually not a permission issue, so the error message should be improved to point to the exact cause (missing screen) or at least mention there is an issue with the workflow.

Note: Deleting a screen is not possible in a seeded way in Jira when the screen is being used in at least one screen scheme or workflow. In such scenarios, the screen was probably deleted in a non-recommended way (through database manipulation or 3rd party apps).