Before you uninstall the game in frustration, follow this hierarchical fix guide. Start at Step 1 and work your way down.
Ensure your in-game console settings permit the server to send you the necessary version files. cod4x patch v2ff is different from server link
CoD4X frequently forces updates to maintain security and functionality. If your client didn't update properly, you will experience a mismatch. Before you uninstall the game in frustration, follow
When a server is set up, it also uses this same file to verify that everyone connecting is using the same patched version of the game. The server’s version of the file is contained in its /zone/ directory. cod4x patch v2ff is different from server link
The server you are attempting to join has updated to a newer version than your current installation.