Pay Pal IPN Service

Question

Hello,

I recently read this article http://www.c-sharpcorner.com/Code/2004/June/PayPalRegistration.asp

It is excellent, and it solved a couple of problems that I had. But I still have one. No matter what I try, but I always receive an "Invalid" as response from PayPal.

If somebody can help me I'll appreciate it.

 

Sergio