"Page not Found" message on Checkout page
On my checkout page, I get a "Page not Found" message at the bottom of the screen (where the shopping cart initially displays) whenever I enter data into the address, city, state, etc. fields. For some reason, it does not do it for the First and Last name fields, just the various address fields.
The continue button works and the payment forms thereafter work, but it is disconserting to see the error message show up every time the user fills in his address.
I tried deleting the lines of code referring to the cart_wrapper, but then I get an error on the whole page saying it can't find the wrapper.
The code for the Name fields is identical to the address fields, so I can't figure out why they trigger the error, but not the name fields.
This page was created using the Checkout Wizard, so it is not something I did.
What could be causing this?
Attached is a copy of the checkout page.