Both NPrinting 16 Server and NPrinting 17 Engine runs as a separate service in session 0. Having access to this session gives the possibility to see QlikView Desktop opened by NPrinting. This is a great help to understand the cause of many issues especially if they are due to a connection problem.
Environment:
The Interactive Service Detection service is disabled by default on many machines.
Resolution:
Here are the instructions to start the Interactive Service Detection:
1. Open the task manager, go to "Services" in the ribbon bar and click on "Services..." in the lower right corner. The Services window opens.

2. Look for the "Interactive Service Detection". Right click on it and click on start.
If you get an error message saying that the service cannot be start, go to point 3. If the service starts, go to point 5.
3.open the registry key (Browse to c:\Windows\regedit.exe)
4. Look for the key HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Windows\NoInteractiveServices. Right click on it, choose "Modify" and set the value to 0.

5. Restart the Interactive service detection as in point 2.
6. Go to NPrinting and start the execution of a task.
7. The Service Detection icon appears in the lower bar of your machine. Click on it.
8. Click on "Show message".

You will enter session 0 and see QlikView working there.
To go out the session you can click on "Return now".