<p>I'm running Repetier Host v1.6.1 with Repetier Firmware v0.92.9.  My computer is running Windows 7 Pro SP1, 64-bit.</p>

<p>If I set a print going via USB then switch to another user (note: I do not log out), then the pinter's display shows that the command buffer drops from 16 to 0 until it stops printing altogether.  If I switch back to the user that is running Repetier Host then the buffer fills up again and the print job resumes.</p>

<p>Before I updated Repetier Host this didn't happen, I could leave it running while I switched users and the job would run just fine.  I'm not sure why this behaviour has changed, but is there any way to get it to run properly under a background user?</p>

I believe what happens here is that Windows suspends the process running the print job, either due to the program not being in focus, because you switch user, or both.
You could try to
increase the priority of the print process in task manager
, and see if that helps.
In Windows 7:
Open Task Manager
In the
Applications
tab, right click the application, and select
Go To Process
, which will take you to its background process in the
Process
tab.
Right click the process, go to
Set Priority
and select some priority higher than the current level.
In Windows 10:
Open Task Manager
In the
Processes
tab, right click the application, and select
Go To Details
, which will take you to its background process in the
Details
tab.
Right click the process, go to
Set Priority
and select some priority higher than the current level.
PS:
Avoid setting the priority to Realtime
, as that effectively will give the process full control of your computer's resources, which could kneel your computer if the program is poorly written.