Game Error: Missing .wad file when loading a map

Map textures are stored in .wad files.

If you've installed a custom map that's missing a .wad file, the map will fail to load.

You should be able to download the missing file by searching for it on the Internet.

Once you've downloaded the .wad file, place it in the game's root folder (for example, for Counter-Strike, that would be \SteamApps\<your username>\counter-strike\cstrike).

If you get this error for a stock map, there is a good chance that your local game content is bad.

To fix this you may have to delete your "local content" for that game:

Steam > Games > right-click > properties > "delete local content"

You will have to re-download the local content again when you do this.