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I got that trying to queue from Cyrodiil to Imperial City. After waiting a bit, I decided to end the rask, but just as I was about to end the task I got a loading screen, then after a short pause I arrived in Imperial City.
I just went to queue from Imperial City to Cyrodiil and saw that it shows me as being already queued for-- or possibly in the process of entering-- my home campaign, as though that message had never gone away from the last time I had queued for Cyrodiil. I tried to leave the queue but couldn't, so I queued for a different campaign. Then I got the black screen again, but I decided to just wait it out, and eventually I got a loading screen and arrived in Cyrodiil.
So my advice would be to wait it out rather than force-quitting.