Here is the original code I had in my PHP script:

$header = "POST /cgi-bin/webscr HTTP/1.0\r\n";
$header .= "Content-Type: application/x-www-form-urlencoded\r\n";
$header .= "Content-Length: " . strlen($req) . "\r\n\r\n";

I got an official email from Paypal saying that I needed to upgrade my IPN script so that it uses HTTP/1.1. So here is what I changed my code to, based on their directions:

$header .="POST /cgi-bin/webscr HTTP/1.1\r\n";
$header .="Content-Type: application/x-www-form-urlencoded\r\n";
$header .="Host:\r\n";
$header .="Connection: close\r\n";

Payments have gone through today, as I can see them on paypal's website, but the IPN is no longer working. Any ideas on what to do?