Access on folder my box files of box

Hi at all,
we have all our website on a folder fo program "Box" to syncronize all of content.

After we have install windows 8.1 we can't see in localhost our website.
The problem is securely the autentication of user, but we have set authentication also for user IIS_IUSRS, but it doesn't works.

If i try to move a website in another genric folder, then localhost works.
So the problem is the folder of Box.
Software Box has a default folder named "My Box Files" where we have all of website and related files.

Can you help us please?

Tx a lot!