Pah, the error's back - some files on my SD Card or Internal memory have weird (almost chinese looking) characters replacing the last letter of the title or author.
When editing to replace them, I get the error message:
Traceback (most recent call last):
File "site-packages\calibre\gui2\library\models.py", line 1089, in setData
AttributeError: can't set attribute
....and once it's finished doing its 'Jobs' and I disconnect, wait, and reconnect... And oddly enough, this time it hasn't obliterated the Collections list on the reader, and it hasn't saved the changes.
I give up!