A common problem encountered when Wing FTP Server was setup as system service on windows, the instance of Wing FTP Server are running under the localsystem account. So it does not get to see the network share resources, there are two solutions here:
1. Changing system service's logon account
Navigate to the Windows Control Panel and select Administrative Tools. Open Services. Look down the list of
services for the Wing FTP Server, and double click on it. Click the Log On Tab and change the radio button to"This account", enter a correct user account in your system and his password, then press OK.
Then restart the service, by right clicking on it and selecting "Restart".
Ok, right now you can add a user directory for network share resources!
Note: Windows services can't recognize mapped network drives by letter for some unknown reasons. So you can solve this issue by the second solution.
2. Installing Wing FTP Server as a normal application
When Installing Wing FTP Server, please uncheck the option "Install Wing FTP Server as a system service".(if you already installed Wing FTP Server,please reinstall it)