Ok Chaps,
The issue has been fixed. The problem was that the show had somehow got copied onto more than one other show and many duplicates and crossovers had confused the system.
I ended up moving and resorting, deleting etc most of the TV shows on that particular hard drive and rebuilding the main library folder on that hard drive one show at a time. THose that had not been corrupted were fine and stayed.
However, it also showed up a number of shows that had issues with files and duplicates. Those have been removed so I can sort them out at my own pace.
My deepest thanks to Jays Plex7 for suggesting I look for duplicates and do the plex dance which I already had done to no avail. Also thanks to those whose help and advice led to a fixing of my issue.
Normal service has been resumed here with the plex server. LOL.
No duplicates to be found anywhere!
Thanks guys for all your help and advice. I have now pinned a note above the server that tells me not to do plex stuff when I am tired and it is late at night!
Snapdragon