I would suggest to remove Gantry completely (remove library, component and system plugin) and install it from the beginning manually. Actually, I am surprised that you didn't already try something like that on your own already :shock:
Also, try to remove the template completely and install latest version from the beginning
If that won't work then I would say we have a problem with your web server which is IdeaWebServer. As far as I know this is some kind of Apache fork but not exactly the same as Apache