I've completed all of the necessary achievements and job quests to unlock Mentor for DoW/DoM (including the 1000 instances, 300 comms), but when I go to do it - I get the "Unable to accept mentor certification at this time." message.

The NPC even acknowledges me, and gives me the prompt, but when I check the box and click accept, I get that. I don't understand what's wrong, please help!