I downloaded the latest version of neolemmix from the website, by clicking on "Latest stable NeoLemmix Player: V12.2.0"
It had the editor included in the file, and I had installed it in a brand new folder.
I open the editor and this unhelpful error message, with Dutch in it shows up:
Selecting yes doesn't open the editor.
This seems to have been fixed by downloading the seperate styles folder from the website and merging it with the one that had been included.
The error message here says nothing to indicate that would fix it.