@mandlair I would start fresh and determine where the problem is manifesting.
Boot up pc. Open device manager. expand Ports (Com & LPT) and take note of whats listed there.
[1] While Device manager is open, turn on your scanner (usb connected) and you should see Device manager update after a few seconds and see "Uniden Serial Port (COM X)" where X is the com port number you assigned.
Proceed to open Proscan.
[2] If your com port config is correct in PS, then you should
not see a com in use message. If you
do, then proceed to check the com settings in PS.
Click the Comm Port menu button. In the Com port settings window, click the Refresh button.
[3] You should see the scanners com port now available in the drop down list of ports. Select it and click the set button.
If no other software (antivirus, HIPS or
other scanner software) is blocking Proscan or using the port, your virtual display in
[4] PS should light up and display what is on the scanners display.
If you have any problems with 1 thru 4 please let us know which step so we can further narrow down possible cause and resolution.