Can not duplicate screen on iMac 27 inch, Mid 2011 using a 2nd Gen Apple TV

Hi everyone!

I need help to duplicate my screen using a 27 inch iMac Mid 2011 using a 2nd Gen Apple TV (Model MD199LL/A)), both using the latest software available up to date (Mac OS X Mavericks 10.9.5 and 7.0(6897.5) respectively).

I have restarted each one of them, including my WiFi router with no use.

The problem started after a Mac OS X SW update a few months ago, and unfortunately I do not know which version was.

I have looked into the forums but it seems there is no a question describing my problem.

Any help and advice is welcome.

Best / Jorge