Did you bypass with RFOM and then use the new Cod4 gamesave for the hacks? I had this problem.
I deleted the cod4 patch and gamesave, then bypass with RFOM. I then chose play online and a new gamesave was created. I copied it onto my USB and put my hacks onto that gamesave then bypassed again and it worked. Also just keep looking for a cage match, it took me 15 minutes before I got anyone to join