Instructions
Delete your current version of the crack. Programs and files, including cracks, can become corrupted for a variety of reasons. When an error occurs, it's often best to remove the crack from your computer altogether.
Patch "Call of Duty: Modern Warfare" to its latest version. Patches are available for free from several file hosting sites, such as FileFront, FilePlanet and other "COD4" fan sites, and will often fix a variety of bugs and glitches that prevent the game from running properly. Even though your crack may not be officially endorsed by the game's developer, they could fix an error that is preventing your crack from running properly.
Download the newest version of your crack. Each time a patch releases, you will have to download a new version of the crack that is compatible with the options and security checks installed with the newest patch. If you try to run a previous version of a crack, it will often crash the game or not boot at all.