Ok - it as I expected.
Highlight the item in Content Manager. RMB>open in explorer. Open config.txt. Find the thumbnail container. Change the 'width240' and 'height180' lines so that there is a space between the word and the number, as in my first post above.
Save config.txt (overwrite). Close explorer window. Highlight asset in Content manager, press CTRL+M to commit back. Errors should be gone if you have done it right.
Repeat for the all the other coaches.............
Good luck!