CoD 4 Mutliplayer "Error during initialization"

Solution 1:

You probably used someone else's config files or deleted the profile data from your folder.

This error occurs when the game expects a profile used in a previous state (e.g. before you copied it) and the profile data are missing, because they weren't copied over.

Check your installation folder for your config_mp.cfg. It should be here:

Drive:\your cod4\players\profiles\name\config_mp.cfg

Inside is a line that looks like this:

[E:\Games\Call Of Duty 4 - Modern Warfare\players\profiles\*some name*\config_mp.cfg]

Make sure the location of your config is identical to this line. The location provided in the config must exist.

If that still does not help you could try deleting your profile from the in-game menu and creating a new one (depending on your game version).

The last resort is reinstalling the game from scratch, but that should not be necessary.