I ripped a CD with five tracks and, since it wasn't found automatically, did a copy of a cover found in Google Images. I selected all tracks, right clicked, selected cover art/paste from clipboard. MC tagged four tracks, but not the first. I tried to copy to just the first track without success.
The album view shows the big blue note. (I'm guessing it depends on the first track-image.) I right click on that, do cover art/find on internet. The desired cover appears. When MC says it has completed tagging, the cover disappears. (I suspect the image which briefly appears is already on my computer--making things more frustrating--and it disappears when MC learns it can't find it on the internet.)
I randomly copied another cover from my own collection and pasted from clipboard. The big blue note remained serenely undisturbed. Not even a temporary image change. I've tried deleting the album and re-ripping and tagging, and various other experiments, without success. Any suggestions? I suspect it's a file naming problem, but I'd rather not go down that path (no pun intended) in my current state of ignorance.
A fact which may be pertinent is that the album is a re-release, and the first track was originally in a different album than the other four. Maybe there's an unusual tagging or format conflict?