When a program runs as a service in Windows, it cannot see "mapped" network drives.  The mapped drive is something that is only available to your logged in session in Windows.  The service is running under a separate unrelated account.  Windows XP had a hack for this, but this was discontinued on all newer versions of Windows.


To fix this, go to your services control panel, find CrushFTP Server, and get properties on it.  Set the service to specifically log on as a domain user account that has access to the areas you need.  Then restart the service so it takes effect.


Next, use Windows Explorer and navigate to the folder you want to add to a user…but use UNC paths to get there.  

{{{Example: \\servername\share\folder\}}}
 
Open the CrushFTP user manager, select the user you want to add the folder to.  Drag and drop the folder from Windows Explorer into the "User's Stuff" area in the user manager.  CrushFTP will then add in the UNC based location for the folder, and as long as the domain account the server is running under can access that location, everything will be fine.