You have set up Windows Authentication to access NiceLabel Control Center. Control Center uses your Windows login for authentication. Based on your permissions, you can use files in the Documents section.
But you cannot access the Documents from the Windows Browse window, or when connecting to Documents from Windows File Explorer. When clicking the shortcut Document Storage in Favorites, Windows prompts you for your username and password, and your credentials are not accepted.
When Control Center is set up to verify users against Windows Authentication, you shouldn't see any login dialog box. Control Center must simply re-use your Windows logon data (when the Control Center runs inside the local intranet).
The problem might be caused by the incorrect order of modules inside IIS.
To solve the problem:
Go to the computer where you have installed NiceLabel Control Center.
Open Internet Information Services (IIS) Manager.
Click the computer name.
Double click Modules in the main window.
Click View Ordered List... in the Actions pane.
Click Move Up in the Actions pane until the selected module is positioned above WebDAVModule.
Close Internet Information Services (IIS) Manager saving changes.