the latest version of the fix if "V4" is outdated for your game build.
By mimicking the game Spacewar (AppID 480) , it opens up the Steam overlay and invitation system. RON_V4_FIX_STEAM_GEN.rar
You may need to manually "install" Spacewar by typing steam://install/480 into your browser or the Windows Run dialog. the latest version of the fix if "V4"