array_key_exists() on Marketpress pages


I installed wpbook today to see if I could set up my marketplace page as a facebook app. All works well. Except I am getting this error: Warning: array_key_exists() [function.array-key-exists]: The second argument should be either an array or an object in /home/fondelif/public_html/wp-content/plugins/wpbook/wpbook.php on line 1146 on every page with marketpress on my site and on facebook.

My very crude guess is that this function array_key_exists() is already used by marketpress? I'm not sure. But would you know of a way to resolve this?

I like that wpbook takes you out of facebook to your site when you click any link. I have tried the wordpress tabs manager and that keeps your whole site in an iframe in facebook.