Thanks for your help everybody...
What is installed :
Code:
Calibre 2.24.0
Kepub 2.3.3 (2 times)
KoboTouchExtended 2.3.3
EpubMerge 2.0.5
Find Duplicates 1.6.2
Kindle Collections 1.7.15
Kobo Utilities 2.0.5
Manage Series 1.2.8
Modify epub 1.3.12
Quality Check 1.9.11
With the help of your comments, I remembered a fact : I met few weeks ago a problem with the KoboTouchExtended plugin, I couldn't open its parameters anymore, I think with a quite similar error...
Since reinstalling it didn't do anything, I have deleted a config file and everything seemed to work again...
Maybe I did something wrong ??
(sorry can't remember which file I have deleted...)