I dont know Whether this can solve your problem or not, But this might help.
https://drupal.org/node/2215527
It basically says they have changed the HTTP API and now only HTTP 1.1 is only supported.
Due to the above change, when trying to make an express checkout payment, you get the following
Access Denied
You don't have permission to access "http://api-3t.sandbox.paypal.com/nvp" on this
server.
Reference #18.a85e6cc1.1394550086.2c263a0 [protocol] => HTTP/1.0 [status_message] =>
Forbidden [headers] => Array ( [server] => AkamaiGHost [mime-version] => 1.0 [content-
type] => text/html [content-length] => 285 [expires] => Tue, 11 Mar 2014 15:01:26 GMT
[date] => Tue, 11 Mar 2014 15:01:26 GMT [connection] => close ) [code] => 403 [error] =>
Forbidden )
It has been done very recently on Date: March 25th 2014
official :
https://www.paypal-notify.com/eventnotification/event_details?eventId=4283