Client PCs are win 10 pro

Server Win 2019

Runtime 10.3.0

This message just started popping up 2 weeks ago. We have been using Acuconnect for 2 years without any problems. I initially thought this was a Wan problem. However I can get the error on the local side of the network. The program is sitting at a menu waiting for an accept. The is no file i/o going on. No program changes, config changes or windows patches were applied before it started. Any ideas are appreciated. 

Good morning, mr David Graham

Is there any sub-program or sub-routine called in thread that may be doing something else, beside the ACCEPT?

The message is shown when acuthin.exe does not receive any answer to his "ping" towards the server runtime.
This occurs because either the runtime is busy doing something, or the communication between acuthin.exe and acurcl.exe/wrun32.exe is lost.

What happens if you click on the CANCEL button?
Does this popup return after another 30 seconds?

Does the application return to work after some attempts, or is it gone forever and you have to restart it?

Can you find the server runtime process and see if it's actually running or it's been closed?

Last but not least, Win 10 has a native process to kill idle connections.
I suggest you to check this setting.