New Post: Big error 404 file not found

If you change the %2f in the url parameter to / does that solve the 404 error?

for example enter the following in your browser:

http://www.xxx.it/Prodotti/Cat-ADMIN/ctl/AdminCategories/mid/427?SkinSrc=/DesktopModules/NB_Store/Skins/Dark/Dark

if the admin pages do display then it looks very much like the urlFormat is set to "Advanced" and needs to be changed to "Humanfriendly", but you may need to clear the browsers cache once the change has been made.