Testing a site I'm working on locally. Everything works up

Testing a site I'm working on locally. Everything works up through and including shopping cart. When I click the shipping button I get a page not found error. Looking in the PHP logs I'm getting the following error:

: array_walk_recursive() expects parameter 1 to be array, null given in PHP Warning: array_walk_recursive() expects parameter 1 to be array, null given in /www/wpecommerce/wp-content/plugins/marketpress/marketpress-includes/plugins-shipping/mp-flat-rate.php on line 183

I've got the shipping set to flat, lower 48 is $10 and all others $0. Paypal and MyCred are both configured. Any help appreciated!

Jim