Cover art not shown in WMP

Hi there tried the search for this one but could not find the answer:

I have bought two audiobooks all mp3 files, the files showed coverart but had rather weird names, so I changed the title tag and based on this the file name, using mp3tag of course. After that no cover art is shown, neither in mp3tag nor in windows explorer. However when I open the files in mp3tag I can see a jpg embedded into the tags. So I removed that jpg and replaced it with another jpg, no effect.
I have checked the folders where the mp3s are: no folder.jpg or other hidden files which do cause trouble...

What's wrong here?

now that is weird: tried for almost an hour to get the cover art shown, so I decided to copy the files onto my network storage and tata.... cover art is now there, at least in windows explorer and wmp....

You probably have to start the update function of your player.
WMP still likes to have the file folder.jpg in a folder. If it finds a file with the old image, then it still shows that old one.
So it is advisable (if you use WMP), to regularly delete all files with the name folder.jpg and albumartsmall.jpg and also delete the folder Grafikcache where WMP has its graphics cache.

And all this:it is a player problem, MP3tag behaves as it should.