You can no longer expect a solution to any issue. Hope, yes, but not expect.
Ok, fingers crossed.
n the meantime, with a bit of trial and error, the best I can come up with is:
1. When you add a new TV show, scan the TV series folder as normal - this will download any missing series and episode descriptions and the Mede8er will still show these (any existing art work in the folder for other shows is not lost). Never use 'Menu - Edit' on a folder that the Mede8er has failed to download art for - this just freezes the machine.
2. If you then plug the Mede8er in to your PC and you will see that the Mede8er has downloaded some fanart and folder jpgs but these cannot be read.
3. Delete the corrupt folder.jpgs and replace with a copy of the small image on the left of the main IMDB page for that series (it is just the right size).
4. Delete the fanart.jpgs and replace with any 1920 x 1080 image for that show you find in Google Images (there are usually loads to choose from)
The above means that all TV series in your Mede8er now have a front image, a season image, a big background image and text description of the series and each episode. (If you have more time than me you could even replace all the episode images but the above is just about good enough for me for now).
Scanning the TV series folder does not corrupt the new images you have replaced (so far anyway!). Just don't be tempted to go Menu-Edit or that really does ruin things.
Hopefully the above is useful to someone else.