W3l.exe is missing
In most cases it means that w3l.exe is missing from your Warcraft III directory. The file is essential for letting you connect to our servers but it may also be falsely detected as a virus since it is a "hack" which redirects the game to our PVPGN servers instead of the official ones. Usually Avast does that.
Add w3l.exe to the exception list of your antivirus and reinstall the Client.