Can't get Lightburn to see my laser on Ubuntu 20.04

[SlickRooster (Karl Kuehn)]

This looks promising:

Port Failed to Open Already in use? Error Message

I had the same error message with my home made laser running Marlin (marlin version 2.0.7.2). Reverting back to v1.2.04 worked for me to get communication with the laser working again. Neither 1.3.00 or 1.3.01 work at all, no matter what other remediation steps I tried.

I mean, in a two steps forward, 3 steps back kind of way. I’m running 1.4 currently.