This can be one of the most frustrating errors because your UNC path may work from some computers but not others. If you are receiving this error the following steps should solve the issue.
Go to Control Panel
- change the view by to small icons
- select "User Accounts"
- select "Manage your credentials"
- select "Windows Credentials"
- then "Add a Windows Credential"
Now enter your UNC server and share path for example: \\UNCServer\SharedFolder
Username and password, then click OK.
Now you should be able to access your UNC share from the windows explorer shell.