PayPal 7 October 2013 Upgrade
If you use PayPal IPN then you will need to patch the IPN code.
It should be located under a folder called /ext/payments in a file called standard_ipn.php or ipn.php.
Look for this code around line 46
$header = ‘POST /cgi-bin/webscr HTTP/1.0’ . “rn” .
and change the HTTP/1.o to HTTP/1.1
$header = ‘POST /cgi-bin/webscr HTTP/1.1’ . “rn” .
that should handle the change.
If you do not have a file in /ext then look in the main code for a reference to HTTP/1.0 and make the change there.