Hi David,
I am sorry to say that I have no solution for you as I came here to ask the exact same question.
Like you, my machine was working just fine (mine is a LC6090 with a Leetro MPC6525 controller, running from LaserCut 5.3). Then yesterday the machine refused to work.
My supplier (G.Weike) in China recommended uninstalling the software and reinstalling it again. This has not had any effect. I have not attempted a firmware upgrade yet.
I am assuming that you are not able to run a contour line either (Test button).
I also eagerly await some advice on solving this problem.