I logged into my Sandbox account, Clicked on "Test Tools", then clicked on "Instant Payment Notification (IPN) Simulator."
I entered the address of my IPN Handler URL, and clicked "Send IPN". The IPN was successfully sent.
BUT, my IPN listerner writes the following to the log file:
"9/3/2011 7:23:47 PM: Error in IPNHandler: amount = ""
IPN code is attached