Warning: in_array() [function.in-array]: Wrong datatype for second argument in ...././.../wp-content

Hi Guys,

After activating the marketpress pluggin on a WPMU site i'm getten this message when i'm going to products.

Warning: in_array() [function.in-array]: Wrong datatype for second argument in /mydomain.com/wp-content/plugins/marketpress/marketpress.php on line 736

Cheers

Dennis