paypal ipn 403 http forbiden

[eluser]Ngulo[/eluser]
hi all guys

when i try to valide ipn returning from sandbox.paypall.com i see in my log file always:

Code:

Destination host forbidden

[12/08/2010 7:52 PM] - FAIL: IPN Validation Failed.
IPN POST Vars from Paypal:

IPN Response from Paypal Server:
HTTP/1.0 403 Forbidden
Date: Wed, 08 Dec 2010 18:52:14 GMT
Server: Apache
Content-Type: text/plain

i'm using CI Paypall_lib

any idea of my problem which is?

thanks