Error Message: "airplay tv is in use by someone else" Please help?

I.m trying to use Airplay Mirroring to stream content from my iPad 2 to my HDTV.

Already using Airplay TV successfully to stream content from my iTunes library using the Remote control but now I want to add my iOS devices but I'm getting the following conflict / error message when I try to turn mirroring on on my iPad 2:

Error Message: "airplay tv is in use by someone else"

Please help?