"The remote computer could not be found" while connecting via VPN

[Spark Blender]

The RemoteApp Tool is working great as long as I'm within the LAN, but I'm having trouble getting it to work remotely over a VPN.

These are my scenarios:

Locally:

1. I installed RemoteApp on my Windows 10 desktop.

2. I generated the Application.rdp file to share one of my apps.

3. I'm able to connect to the app, using the Application.rdp on my LAN.

Remotely:

1. I'm using OpenVPN to connect to the business network remotely.

2. I'm able to connect via Windows RDP to my computer successfully.

3. I disconnect the Windows RDP session.

4. Next, I double-click on Application.rdp

5. The initial standard RDP warning window pops up, but then, after acknowledging that, I get what seems to be an application-specific message:  "RemoteApp Disconnected. The remote computer could not be found. Please contact your helpdesk about this error".

I tried disabling firewalls on both machines, to see if that's an issue, but no joy.

Any ideas on what I'm missing or what else to try?

Thanks. 

[Spark Blender]

After much trying, I've been able to find out what the problem was:  

Under the 'Host' tab, both 'Server address' and 'Alternative server' had to be set to the IP address of the machine (see attachment).  I had entered only the IP address in the 'Server address' field, and left the 'Alternative server' with the machine name (default), which I thought would be ignored anyway.

I have been assuming that the 'Server address' is the address for the machine hosting the app, without actually knowing what the 'Alternative server' is for.  

Does anyone know what the difference between these two fields are?  i.e. what's their individual purpose?

Thanks.