If you play on Team Fortress 2 servers from multiple communities, or a map is updated on a server with its filename unchanged, chances are you will get this error. This occurs when the map file you have on your computer is not the same as the server's, for TF2 cannot overwrite map files. To fix this, you will need to delete the existing map file manually. Here's how: Navigate to your TF2 installation folder. This is usually located at Program Files (x86)/Steam/steamapps/common/Team Fortress 2. Look for the map file causing the error in both tf/maps and tf/download/maps. Delete any instance of it, then try connecting to the server that gave the error again. The correct map file should download. If not, try restarting TF2.