I spent a few hours today setting up a simple shopping cart using the wp-shoppingcart plugin.  I entered a few products, set up the PayPal configuration and attempted to make a mock purchase.

The PayPal site greeted me with the following message:

"Return to Merchant
Unable to process payment. Please contact the merchant as the shipping address provided by the merchant is invalid, and the merchant has requested that your order must be shipped to that address."

I googled the problem and found the WordPress help topic addressing this issue at  http://wordpress.org/support/topic/153679

Unfortunately the information and the file identified as being at   /includes/modules/payment/paypal_ipn.php  turned out to be incorrect. 

Searching through the shoppingcart plugin revealed the code at wp-content/plugins/wp-shoppingcart/merchants/paypal_multiple.php  Open the designated file and scroll to the area shown in the graphic below.

Locate the highlighted line and comment it out as shown.  If you use  WeBuilder 2007 for your php edits, the line numbers shown should be accurate.  Save the edited version of this file and all should now work with PayPal.

Try it out and let me know if you find any problems.