You get a server rack ... and you stick windows on it?!?! facepalm
Thats issue number one.
You should have a linux distro witrh mysql, php and the other bells, whistles and whatever floats your boat.
Then the system would work with anything.
Have you checked the server logs to get a better understanding of why you are getting this issue in your setup.
last time I used a window box for a server was a long while ago, must be 20 years now. So I would suggest that you check the path settings, if you have any PHP.ini files you can tweak to ensure that everything is battened down and your belts and braces approach will ensurte that theirs no doubt that your setting the right paths.
Now as far as I can recall, paths under windows...
if you have lots of these \ then you are a path on a local machine and I always had issues when \ wasn't \ in the local paths
if you have lots of these / then you are a path on a remote machine and always had a problem when \ was returned as a path and it won't mix with /
So if you are getting a "local path" which is returning a path with \path\to\file and you are appending \path\to\file/intranet/common/light_me_up_baby.php to that absolute path with relative addressing, then you are going to have issues if the path can't be resolved properly... so as for calling the required files, why not just use paths relative to the root if your root folder has the "intranet" folder accessible to the other scripts, for example...
require_once("/intranet/common/core-settings.php"); over an absolute path, this is often where problems do arise and best off only using absolute paths when relative paths are not working, this is often a translation of links in servers and best left to the server until it needs a hand.