I'm betting that with more use you have found that although pixelCNC looks like it is running fine at first, it actually still has problems that make using it in linux impossible. I have tried it on Debian 9.0 using wine as well and found it would freeze up and other problems (can't remember everything it wouldn't do now). I got the same error message that you did and I could get it to run by clicking OK but it ran into problems when I actually tried to create a toolpath. I wasn't using Wine5 though, so if you have found a way to make it run properly in Linux I would love to know how. That way I wouldn't have to keep switching between windows and linux on a dual booted machine. I actually installed win7 on this machine just so I could run pixelCNC. Its such a useful program and getting better all the time....Im having a lot of fun with it and I wish it ran natively in Linux....hope you are too.