Widgets are not editable and contain error message

Hi all, It looks like I may have got some corruption on a client’s site via a bad plugin. Seems to be affecting the widgets.php file. Here is the error message:

Warning: array_key_exists() [function.array-key-exists]: The second argument should be either an array or an object in /home2/virtuosi/public_html/charlesriverrecruiting/wp-includes/widgets.php on line 858

The problem is how do I fix this without doing a clean install of WP?

Here’s the URL: http://www.charlesriverrecruiting.com/

I’ve already updated WP to current version, updated theme files, replaced the plugins folder with a new empty one, replaced the widgets.php file several times and repaired the tables in PHPadmin. Anything else I can try? Thanks so much!