error message while updating plug-ins

Help! I upgraded wordpress to most current version. I did back up everything before I upgraded (thank God). after the upgrade, everything seemed fine except that the Event Espresso calendar was not showing on the calendar page. After reading the ee forums about this problem, they suggested that I needed to update all the plugins, in case of conflicts between various versions. (it had been a long time since anything had been updated on the site.) Stupidly – I was quickly going through the list and hitting the “update auto” buttons. suddenly got the following error:

Fatal error: Class ‘Genesis_Admin_Basic’ not found in /home/betalefo/public_html/wp-content/plugins/genesis-simple-sidebars/includes/admin.php on line 14

and now I seem to be totally locked out of the back-end. The site itself is still up – but when I try to log in as admin, I get a white page with the fatal error message.

I really can’t even tell you which plugin that caused the problem. (I know – how dumb) If there is anything I can try before I have to re-install the back-up, I would so appreciate the help.
the site is betalef.org