I've no idea what this warning means?

Hi folks

This is the warning I'm getting;

Warning: array_key_exists() [function.array-key-exists]: The second argument should be either an array or an object in /home/lgmsites/public_html/wp-content/plugins/advanced-theme-switcher/advanced-theme-switcher.php on line 106

I've found the .php file and opened in notepad and found line 106......so an y ideas on how I fix this now?

Many thanks for any help you can give.

lgm