Why can't I export my game to windows?

I can't export my game to "PC, Mac and Linux StandAlone". I don't know what to do as I have exported other games. But now it says "Build path contains project built with "Create Visual Studio Solution" option, which is incompatible with current build settings." even though I haven't touched anything. I tried changing the Architecture from 86_64 to 86, but it didn't work. Are there any fixes to this?