"Call of Duty" is unable to load the default CFG because the game cannot locate the "Main" directory. This error occurs when the game is installed in a root directory, such as "C:" rather than a subfolder. To fix the default CFG error reinstall the program into a subfolder."
A recent system restore is also known to cause this issue. This modifies the registry entries for the game, causing it not to load. If you have manually modified any registration entries, this also causes the default CFG error. To remedy this, uninstall the game through the "add/remove programs" utility in control panel. Next, reinstall the game. This process renews the registry entries and solve the error.
Default CFG error can also occur with the Steam version of the game. If you own a Steam version of "Call of Duty," go to the Steam menu. From here, change the language from English to Spanish, and back to English again. This should fix your Steam version of the game.
If the above methods fail to solve the issue, please contact official Activision support. It offers walkthough guides to solve problems, as well as social media forums where other "Call of Duty" players assist with troubleshooting.