i had this error frequently while using ZendAMF. It was always a Problem with the PHP code. Some call to a method which did not exist, a class method call without $this, or any other minor thing which should cause PHP to send a warning, but in conjunction with ZendAMF (since error_reporting needs to be turned of to have it working stable) the PHP script sometimes just dies without any warning/error written.
So my guess, just check back your PHP code (make a Unit test, etc). hth martin
