i think the printer is just angry at how dirty you've let it become
there's a magnet that holds the clip in (or the cover-down, if the clip was screwed to the cover), on the printer just behind those two holes on the cover. sometimes it shifts, and even though it is still there, it might not be making the connection intended.
also, the silver cap/cover that surrounds the capping station and heater switches & button... has a similar cap/cover on the left-side of the printer. that entire cover is also a "clip" that is intended to make a connection when screwed-in properly otherwise this cover/switch will also throw a "cover open" error.
*EDITED: WOOOT! 3000 posts! Fitting that it was on a mimaki topic, as that's where at least 2k of them were from over the years.