Figured it out...
Seems obvious but I wasn't sending the full file path to the "filesize()" function... I just assumed that since I had alread opened the folder, PHP would pretty much understand that the file I was asking it to get me the filesize for was in that folder.. apparently not.. 😉
I know I know... code ain't smart... 😉
So, it wasn't an issue with mapped drives or anything... I just wasn't passing the whole path, just the single filename...
B.