sort of makes sense to me as I was sent the following from the paypal forum:
"I am still not sure what the error is that you are getting. The request you provided, is for the SetExpressCheckout API. This would be the first API done. Then you would be redirected to PayPal where you would sign in and select your information and agree. Then you would be returned back to your site, where it would do a GetExpressCheckoutDetails API call (this api call is optional), Then you would get a response back. Then your site would do a DoExpressCheckoutPayment API call. This is the final API call that tells PayPal to process the payment. Are you making these other two API calls from your system?"
Looking at my own issues it would seem that mine is failing at the Getexprresscheckoutdetails API.
I agree with you we seem to be stuck in the middle. However I'll add this paypal question to my own tech thread and hopefully we can get a resolution