File Version
Battle.net scans your ̶0;Diablo 2̶1; game files to verify you̵7;re running the latest version. If Battle.net identifies your version of ̶0;Diablo 2̶1; as an older one, it automatically downloads the latest patch and updates for you. The ̶0;Unable to Identify Application Version̶1; error message occurs when Battle.net can̵7;t identify your game files. Your ̶0;Diablo 2̶1; files may be corrupt or altered. Battle.net only allows you to connect if you̵7;re running the latest official version of ̶0;Diablo 2.̶1;
Immediate Solutions
Blizzard recommends trying to reconnect several times if you see this error message. The error may be caused by a temporary connection problem. If reconnecting doesn̵7;t help and you̵7;re using Windows Vista, Windows 7 or a newer version of Windows, Blizzard recommends running the game in administrator mode. Close ̶0;Diablo 2,̶1; and then right-click the ̶0;Diablo 2̶1; shortcut on your desktop or in your Start menu and select ̶0;Run as Administrator̶1; to launch the game in administrator mode.
Game Disc
Third-party ̶0;no CD̶1; patches or programs that alter ̶0;Diablo 2̶1; files to run without the game CD in the computer's optical drive can also cause this problem. Uninstall the patch or program and restore the original game files if you̵7;re using one of these programs. You can still run ̶0;Diablo 2̶1; without the original game disc in the drive by updating to the latest version of ̶0;Diablo 2,̶1; which removes the requirement. Copy ̶0;D2Music.mpq̶1; from your ̶0;Diablo 2̶1; or ̶0;Diablo 2: Lord of Destruction̶1; expansion disc to the ̶0;Diablo 2̶1; installation directory to run without the game disc if you performed a full installation of the game.
Virus Modification
Viruses that modify the files on your system can also cause this error to occur. Blizzard recommends running a virus scan and cleaning any infected files, particularly if you receive this error again after reinstalling the game. If you don̵7;t have an antivirus program, you can download a free one such as Microsoft Security Essentials, AVG or Avast! from the Microsoft, AVG or Avast! websites, respectively.
Reinstalling the Game
Blizzard recommends performing a full reinstallation of the game if you can̵7;t fix the problem. Uninstall ̶0;Diablo 2̶1; from the Windows control panel, insert the game disc into your disc drive and follow the instructions on your screen to reinstall it. If you have the ̶0;Lord of Destruction̶1; expansion, install it after the original game. Download and install the latest patch for ̶0;Diablo 2̶1; from the Blizzard website after reinstalling the game.