Access Denied error when attempting to consume web service

I am attempting to call a web service from my extender control, but when I do so, I get an error message - access denied (there are no other details). After some research, I think this has something to do with cross site scripting - since the web service exists elsewhere (it is a public webservice). How does one access an external webservice?

Here is the code that is throwing the error:

Sys.Net.WebServiceProxy.invoke(this.get_servicePath(),this.get_serviceMethod(),false, params,

Function.createDelegate(this,this._onMethodComplete),

Function.createDelegate(this,this._onMethodFailed));

ServicePath="http://www.webservicex.net/uszip.asmx"ServiceMethod="GetInfoByZIP"

Check out this article:

http://dotnetslackers.com/columns/ajax/MashitUpwithASPNETAJAX.aspx

Hope this helps,

Elias.