Unsafe JavaScript error writing to C# variable

I have some JavaScript in a page that takes the values passed by a module Window and assigns it to a C# variable, so it can be used within the code behind. So my JavaScript looks like:

The JavaScript

<script type="text/javascript">

       function openSecure(args) {
           var manager = $find("<%= rwmSecure.ClientID %>");
           var domain = '<%=ConfigurationManager.AppSettings("CPCDomain").ToString %>';
           var URL;

           if (domain == 'localhost') {
               URL = 'http://localhost';
           }

           URL += "/WindowPage.aspx?args=" + args;
           manager.open(URL, "rwSecure");
       }
       function OnClientCloseSecure(oWnd, args) {
           var arg = args.get_argument();

           if (arg) {

               var ResultCode = arg.ResultCode;
               document.getElementById("hdnResultCode").value = ResultCode;
               var AuthCode = arg.AuthCode;
               var ReferenceNumber = arg.ReferenceNumber;
               var TransactionID = arg.TransactionID;
               var ErrorCode = arg.ErrorCode;
               var ErrorDescription = arg.ErrorDescription;
               var CardNumber = arg.CardNumber;
               var PONumber = arg.PONumber;
               //document.getElementById('<%=btn.ClientID %>').click();

               __doPostBack('pnlComplete', '');
           }
       }       
</script>

And to clarify this a bit more. The Module window is pulling in a page from localhost, but the Module window is being called from a page on localhost:61156. So once the javascript sets the variavle it also issues a click command on a asp.net button to run some code:

C# Code

protected void btn_Click(object sender, EventArgs e)
{
    if (string.IsNullOrEmpty(hdnResultCode.Value)) {
        dspConfirm();
        pnlComplete.Visible = false;
        pnlConfirm.Visible = true;
    } else {
        dspComplete();
        pnlComplete.Visible = true;
        pnlConfirm.Visible = false;
    }

}

So when I run this I get a javascript error that says:

Unsafe JavaScript attempt to access frame with URL http://localhost/SecurePayment.aspx?args=H4sIAAAAAAAEAOy9B2AcSZYlJi9tynt%2fSvVK1%2bB0oQiAYBMk2JBAEOzBiM3mkuwdaUcjKasqgcplVmVdZhZAzO2dvPfee%2b%2b999577733ujudTif33%2f8%2fXGZkAWz2zkrayZ4hgKrIHz9%2bfB8%2fIr578jMnL09%2b5k3etG%2fqbNlk07aolj%2bzi%2bdndsY7u%2f9PAAAA%2f%2f8VkT5ZIQAAAA%3d%3d&rwndrnd=0.23641548841260374 from frame with URL http://localhost:65116/ShoppingCart.aspx. Domains, protocols and ports must match.
b.RadWindow._registerChildPageHandlersScriptResource.axd?d=vMihE91hOtu6KBE47c3D9AjqD9Il5YI4LpCLhSvp5YZn6p98cl2a_AbJJmNWVZfnmjtLnCnYEoaBHBC919OsikIEmKq8TGOzWNWN_HUBLLo8fW7DdN4EuN3Q076lAa_FOwh_Yk2b3DL-W2Fv0&t=38ec0598:1125
b.RadWindow._onIframeLoadScriptResource.axd?d=vMihE91hOtu6KBE47c3D9AjqD9Il5YI4LpCLhSvp5YZn6p98cl2a_AbJJmNWVZfnmjtLnCnYEoaBHBC919OsikIEmKq8TGOzWNWN_HUBLLo8fW7DdN4EuN3Q076lAa_FOwh_Yk2b3DL-W2Fv0&t=38ec0598:1143
(anonymous function)ScriptResource.axd:47
Sys$UI$DomEvent$addHandler.browserHandlerScriptResource.axd:4048

So is there any possible way around this or way to fix this? I've been scratching my head for two days and I'm ready to throw my keyboard. :) Thanks!