Files from Heroes 3 are missing. Please reinstall Heroes 3.

Basically, I installed Heroes of Might and Magic 3 Complete and it only runs as administrator, which prevents me from playing online with friends through GameRanger. If I just launch it normally, it gives me the error: "Files from Heroes 3 are missing. Please reinstall Heroes 3." I've reinstalled it, but it didn't help. I've searched the internet and can't find a proper solution anywhere. I'm not sure what else to do. I also tried setting compatibility with Windows 95 and 98 in the properties, but it still only works when running as administrator.