OK, so I'm guessing I've done something stupid. Windows 2012R2 with IIS etc

Been developing a new website in a folder off the webroot called 1. All working fine. Finish the development and move the entire structure down a folder into the webroot so it goes live. Everything is working fine apart from this php code I've been using to display files and folders in an iframe (neater than just turning on directory browsing) Encode Explorer :: A simple PHP file browser

Now I get a 403 14 0 15 error when I try and browse into sub folders. The folders just contain pdf and office files.

I've been looking but can no longer see the wood for the trees. Any suggestions as to what I've missed?

Yours feeling very dumb