We have discovered this few days ago. Newest version of mono (as any above and including 4.0.5, 4.2.1 especially) has introduced feature/bug, which causes issues with communication on the line PicoScope6 <-> drivers. The workaround/fix has been proved to work, now we are looking into preparing another release including those fixes.
In mean time you could try to use older version of mono; 3.12.0
works for me.