Strange problem in back end

Just one other thing : Do you believe if I update CK slideshow it might resolve the problem, and will it erase my work ?

no it will not solve this problem, as this is related to the NN framework and I don't know what it is
then updating will not erase your work, only if you uninstall it

Just wanted to thank you for pointing me in the right direction. Deinstalling NoNumber Framework plugin and disabling tthe rest did the trick.
The guy from NoNumber told me the path I mentionned should not exist... I don't know what went wrong.
Thanks again !

ok cool, happy to see that you solved it