I don't have time to play around with it right now, I'm just gonna use something else, plus I realize now that it can't do eCheck and it's more important that they can pay by any means for me. I think I'm gonna give DT Billing a try, seems like it's the only one with eCheck capability. Maybe I'll have better luck. I think nBill is better if it worked reliably and had eCheck ability. Thanks for you help.

EXCELLENT Detective Work. It's working now for me too. Hopefully the support team will make the necessary documentation for this and also add in the eCheck capability. Thanks a lot for your efforts.

Perhaps you could try the attached version and see if it resolves these problems. There are a couple of new settings, one of which allows you to enter a proxy IP address and port for GoDaddy accounts.

Thank you for reporting back. To respond to your points:

1) When an order is placed via an order form, the invoice is not created until AFTER the payment has been confirmed, so it cannot pass the invoice number (this is because people often back out of payment and re-submit again, so you don't want lots of unnecessary invoices hanging around)
2) Great
3) It should not redirect you to authorize.net UNLESS you accessed the order form over http instead of https, OR the SSL port number in the gateway settings is set incorrectly (for 99.9% of servers, the default value of 443 is correct). The port number is a new setting in this version of the gateway so it is possible there is a problem there.
4) nBill can be configured to send an order confirmation email to the user, but an actual receipt for payment is down to authorize.net as they are the ones taking the payment.

Ok,

#3. I had put the port number for the proxy (3128) where the SSL port number goes, so once I change the SSL Port back to the defaul 443, it works as expected.