programing 2 remotes to one hd dvr receiver

i have an hd dvr  box that mirrors a tv in another room. the installer programed two remotes to the original box on the rf mode. that allowed me to operate the tv not connected to the receiver with its own remote. 2 weeks ago my receiver stopped working and dtv sent me another box. hooked everything up box works fine, but i can't get both remotes to work. i can program one just fine, but when i try to program the second one it will work fine but knocks out the other remote. i know theres a trick to this, but i can't crack the code. any help wou;d be great. thanks