Call of Duty backup works, but then again

Hello,
I have a playstation at work with the original call of duty DVD and I also have a playstation at home with a modchip. I wanted to use a backup copy at home to play the game, however I have ran into a small problem. I am using anydvd and clone cd to copy the game and the backup copy works great. However when I try to play an online game from the backup it fails the DNAS. I noticed that even if I put the original disc in the DNAS fails, unless I disable my mod in the playstation. Is there anyway around this? Or am I stuck with buying another copy of the game?