You don't have permission to do that.
when it do?
Please answer Why not What.
This is a symptom of this forum's broken escalation/re-categorization process. It happens whenever a moderator moves a question to a behind-the-scenes support queue. It can, I think, also happen if a moderator simply wants to move a question to a different category, but fails to mark the correct checkboxes (or something).
You should get a private message from the moderator telling you what's going on, but I think some moderators still haven't caught on to the consequences of their actions. They still fail to realize that escalating a question renders it and all of its responses immediately and completely inaccessible.
It's that "immediately" that's the particular problem here: your question received a reply, but by the time you were notified and went to look, the moderator's actions had rendered it invisible.
I have the same problem. Really frustrating.