ePub convert ok in 0.8.46, not in 0.8.50

[sjordi]

Hi,
I just upgraded from Calibre 0.8.46 tp 0.8.50 and wanted to try converting a book written from a friend.
It was a Word document saved as HTML filtered.
That .htm file did work flawlessly in 0.8.46. From Zip to ePub, device iPad.

Then under 0.8.50, it fails. The exact same file.
I uninstalled 0.8.50 and reinstalled 0.8.46 and here it works again, giving me the ePub.

Any idea?
Looks like the problem comes form a Unicode string. The text is in French with accents.
The main error says " All strings must be XML compatible: Unicode or ASCII, no NULL bytes or control characters (Error Code: 1)"
I enclose the full error as an attachment.

Any way to know where the problem is actually located?
Thanks for any help.