Remote sync proble on ML

Hi, I've just recived the new iMac 27"...wonderfull, but the remote it doesn't seem to sync with iMac. It work with the old imac, but not with this. I have ML, there isn't anymore "Disable remote control infrared receiver" checkbox in Security and Privacy so, how can I enable my remote? I saw a lot of problem like this to the ones has got the last MiniMac, I guess is the same problem.

Waiting for your help.

Thank you