Hi @k-gosciniak_5741 ,
We've got no clue what's causing that, but definitely some kind of IIS configuration. Ultimately I don't think the request for that file is being passed into ProGet, but IIS is trying to find the file on disk instead (which it obviously won't be).
I would guess if you put a file on disk that file would be served via that URL. IT's just a guess.
Other things to look at ... MIME mappings, I've seen those do strange things. Maybe there's other IIS modules. It's really hard to guess.
It might just be easiest to switch to the Integrated Web Server; you can just uninstall / reinstall ProGet. That won't use IIS then.
Cheers,
Alana