Having CoD problems! HELP

[Looski]

Please someone tell me wat this is.
I went to play Call of Duty I logged into a server fine, but when it got to where I pick allies or axis it disconnects me.
The message says "Unpure client detected. Invalid .PK3 files referenced!"
Wat does this mean, how do I fix it, wat is a pure/unpure server.

The game has worked great until today, I've played multiplayer before on the same server. Some one help.

 

[VicodiN]

You have some kind of modified file... aka custom crosshairs, custom skins, etc.

 

[BlueWeasel]

The server is a "pure" server and is not allowing you to connect because, as VicodiN mentioned, you have some modded *.pk3 files in your COD directory. Once you delete the modified files (not the base .pk3 ones), you should be good to go.