Create a thread.
Try to post with an account with no enough permissions. The post will be up for approval.
Close the thread.
Try to approve the post leads to 500 Internal Server error popup.
Opening the thread again and approving the post worked.
Yes, that is correct. If the topic is closed or deleted, approving the post (in that topic) should not work. I agree that error message can be improved. Done via:
Now the error message will be:
Something has gone wrong. Perhaps this topic was closed or deleted while you were looking at it?