Thanks for your reply Synergy.
I've tried both the dvd-rom files plus the download from MS. Same error pop-up when I click on either the SP or MP icon.
I didn't try running as Admin so I'll reinstall the game and try again :-).
I realize it's an old game but I'd like to finish the SP on Veteran mode. I've got both Windows 7 Ultimate X64 and Home Premium X64 on 2 hdd's. I'm planning on scrubbing the Ultimate and using Home Premium for all my games, etc..
The problem is that COD 4 SP and MP work aok on Ultimate but it...