When trying to access a UNC path in the address bar, you get the following error:
Access to the resource <<UNC path>> has been disallowed.
This is because a Group Policy Object is disallowing the user access to UNC paths. To fix this, configure the following GPO setting to disable removing Run menu from the Start Menu for the user:
User Configuration -> Administrative Templates -> Start Menu and Taskbar -> Remove Run menu from Start Menu
This is because disabling the Run menu in the Start Menu also prevents users from accessing resources in UNC paths in the address bar.