If manual installation doesn't immediately fix your crashing errors, utilize Steam's built-in repair sequence to recover corrupted dependencies:

Modifying or replacing core game files with assets from unauthorized third parties can trigger Ricochet Anti-Cheat flags, leading to permanent account bans. The Best and Safest Ways to Restore MW3 Zone Files

Steam will compare your setup against official servers and automatically download healthy replacements for any broken zone files. 2. Battle.net Launcher

Call of Duty: MW3 receives frequent patches, hotfixes, and playlist updates. Zone files uploaded to community forums are often outdated. Mixing old zone files with an updated game executable results in immediate launch crashes and fatal errors. The Best Legal and Safe Ways to Repair Zone Files