@tparsons: Do you have any working secure page on this domain?
create test.php inside magento folder and try accessing it.
If does’t work, probably .htaccess. rename or remove .htaccess and try again.
if still doesn’t work, it is web server configuration problem.
these steps got website payments pro to work when submitting a credit card for testing purposes (site is not live).
unfortunately, paypal express still does not work… i get an error message once the page makes it over to paypal… where it states the transaction is invalid.