R – ASP Web.config folder path isn’t resolving

I've just been asked to fix an ASP site and I know absolute no ASP. When I try to load the site, I get greeted with the following error:

MENU CACHE EXCEPTION:No menu xml file found for menu id 1. Make sure the xml file \menuxml\menu_1.xml exist.

I've tried editing Web.config to point to the correct folder using a variety of different paths. None seem to work. I keep getting the same error. Here's how it currently looks:

<add key="menuXMLFilesDir" value="/clientsdata/iis7_www/c/a/site/www/menuxml/" />

I figured the problem was it required an absolute path starting from root. I asked for that path and received that in return. To me, that looks very Linuxy. I was expecting to see drive letters (C:…).

How do I point to the correct path?

Btw, the Web.config file and the menuxml folder are both in the document root.

EDIT: I've tried numerous system paths to point to the menuxml folder and also web relative paths. None seem to work. From all the help Stephen M. Redd has given, I'd expect this issue to have been fixed. Since it's not, I can only assume the problem lies outside of Web.config. What else could be done to try and rectify this? :/