Google Checkout setup error

Hi I’m currently in the process of setting up wp shopping cart and I have run into a problem. Whenever I attempt to complete the check out process when I click Make Purchase I get this in return.

Warning: Invalid argument supplied for foreach() in /home/content/h/a/n/hansirudolph/html/wp-content/plugins/wp-shopping-cart/submit_checkout_function.php on line 156

Warning: Cannot modify header information – headers already sent by (output started at /home/content/h/a/n/hansirudolph/html/wp-content/plugins/wp-shopping-cart/submit_checkout_function.php:156) in /home/content/h/a/n/hansirudolph/html/wp-content/plugins/wp-shopping-cart/submit_checkout_function.php on line 258

Warning: implode() [function.implode]: Bad arguments. in /home/content/h/a/n/hansirudolph/html/wp-content/plugins/wp-shopping-cart/merchants/GoogleCheckout-XML.php on line 81

Can anyone please let me know what this problem is?
Thanks in advance for your help.