This doesn't help. I need to see the error code returned to the page by paypal, not the source of the code from Dreamweaver.
The key error is:
SOAP-ENV:ClientXML syntax error
This usually means you have illegal characters in your product name. What product were they trying to purchase? I'd try adding the same items to the cart they did and then you can probably reproduce the error.
The key to fixing any problem is always to reproduce it. If you can't reproduce the problem, then there is no way to ever tell if what you do actually solved the problem at all.