I'm no stranger to using RDP to connect to a server and open a program automatically.
Presently, I'm experimenting with an attempt to connect (from a PC not on our network) to a File Server in our domain on which Quickbooks Enterprise is running and several data entities are stored.
If I'm onsite and connected to our network, I can reach the File Server itself and use a shortcut on the desktop to open Quickbooks. The shortcut's properties show a path which is: "C:\Program Files (x86)\Intuit\QuickBooks Enterprise Solutions 12.0\QBW32Enterprise.exe".
If I paste this same path in the RDP "Start Program Upon Connection" box, I have no problem connecting to the File Server remotely, but Quickbooks will not open automatically. I reach the desktop of the File Server and the Quickbooks icon is on the desktop. I can then open Quickbooks by clicking on the icon, but I don't want end users to be able to see the File Server in any way. That's why I prefer to automatically open Quickbooks upon connection, if possible.
The logon credentials of the end user for the domain are being used in the RDP. The end user is a member of the "Remote Desktop Users" group on the File Server. I don't think this is an authentication issue.