I'm like Bond!
Ote told you to run the demo through game (until you fix this problem). Copy the demo in folder where all your recorded demo files are, and then open cod4 and type in console /demo 'demo name' and game will run it but without that fancy stuff
Just right click on a demo and change the standard program to open it to cod4/iw3mp.exe or whatever you renamed it
This way you just have to double click on a demo to play it...Works for me at least..