There are many, many variables in payment systems. All it takes is one bad or missing piece and it does not work.
After substituting the new file provided (thanks, Alex) something was still wrong. After trying various changes, I was about to give up and turn it over to the pros like 'espresso' did.
So I logged into Paypal/Payflow to set up a new user for test purposes and I discovered a new user type called "API-FULL-TRANSACTIONS".
I went into PayPal's help system to read the purposes of this user type and it was not listed with the others. But it sounded right, so I picked it.
When I got back into X-Payments and was resetting the user info, I noticed that the box for 3-D Secure Payer Authentication was checked. I really don't know if that is part our our account's services, so I unchecked that.
The next test payment worked
, but I'm not sure which of these changes made the difference. So for any of you having a PayFlow problem using X-Payments 1.04, use the update file from the link above, choose the user type "API-FULL-TRANSACTIONS" in Payflow, and try unchecking 3-D if you don't use it.