The Backup doesn't run

Hi,

The backup doen't run with this website.

First I had this message :
Something went wrong with verifying your access rights. Please try again, or reset your secret key.

I reset my secret key (it was good). I have the same ERROR Message.
I have the super-admin right for the multisite and the admin right for the website.

And know, the backup begins and I have this :
See the very short video : http://screencast-o-matic.com/watch/cD6166jva6

I manage the backup from this dashboard before going to the website when I click.
http://screencast.com/t/XTkjc0xkg2a

Thanks for your help.
I don't understand what happens.
Regards
Ludovic