Problem with back-up

Dear support team,

I am currently using WP v3.7.3 (not in the list above) and the iThemes security plug-in v4.2.6.

I want to do a backup of our database, but unfortunatly I can’t manage to do so.

Few days ago, when I installed the plug-in, I launched a back-up. But the process took to long (the button displayed “working…”) and I had some work to do so I cancelled it, thinking that I would launch the backup at night, while noone uses the website.

However, and after several tries on several days, I get the following message each time I try to back-up the database :
“Something went wrong with your backup. It looks like another process might already be trying to backup your database. Please try again in a few minutes. If the problem persists please contact support.”

I use the same plug-in on a different WP site and everything is fine. I get e-mail every two days with a copy of the back-up, but I never received any e-mail for the website euroscientist.com . I installed the plug-in on both websites the same day with the same backup settings.

My guess is that the first backup process didn’t close in a clean way and now it can’t launch another process.

How could I kill the ongoing process in order to make a clean back-up ?

Would you have any other suggestion on the source of the problem ? And a solution ?

Thank you very much for your time and help.

Regards,
Grégoire Llorca

https://wordpress.org/plugins/better-wp-security/