PayPal Express 404 Error

Hello. I'm having an issue with my site where when you click on the button to pay with PayPal Express it displays a 404 page not found error. I check the debug logs and nothing shows up here about the problem. I suspect the problem is probably caused by the fact that I recently bought another domain address and change the configure.php to point to this new domain. So that my configure.php say "define('HTTP_SERVER', 'http://www.dablur.com');" but all my zencart files have not moved from the old domain dabbersdoodle.com. I also have installed the Ceon URI Mapping module. Here is a link to the store.

Currently the standard checkout with PayPal is working but it would really be great if my customers weren't required to create an account to purchase something. Could these URL rewrites be causing the problem? If so, what are my options to fix this?

Thanks,
Hadley

The link to your /ipn_main_handler.php is broken ... either because the file is missing from your server, or because your URL-rewriter has busted normal operation.

Thank you DrByte,

The problem was cause by issues with URL-rewriter and my htaccess. Everything is working properly now.