Question

Not really sure why I’m getting the exception.. the code is sound and the API is working through my browser.

var url = new Uri("http://octopart.com/api/search?keywords=" + topic.Text);
        WebClient octopartCall = new WebClient();
        octopartCall.OpenReadCompleted += new OpenReadCompletedEventHandler(Octopart_Completed);
        octopartCall.OpenReadAsync(url);
 if (e.Error == null)
        ... error is not null so I throw the message below  

System.Exception occurred
Message=System.Security.SecurityException —> System.Security.SecurityException: Security error.
at System.Net.Browser.BrowserHttpWebRequest.InternalEndGetResponse(IAsyncResult asyncResult)
at System.Net.Browser.BrowserHttpWebRequest.<>c__DisplayClass5.b__4(Object sendState)
at System.Net.Browser.AsyncHelper.<>c__DisplayClass2.b__0(Object sendState)
— End of inner exception stack trace —
at System.Net.Browser.AsyncHelper.BeginOnUI(SendOrPostCallback beginMethod, Object state)
at System.Net.Browser.BrowserHttpWebRequest.EndGetResponse(IAsyncResult asyncResult)
at System.Net.WebClient.GetWebResponse(WebRequest request, IAsyncResult result)
at System.Net.WebClient.OpenReadAsyncCallback(IAsyncResult result)
StackTrace:
at Register.Page.Octopart_Completed(Object sender, OpenReadCompletedEventArgs e)
InnerException:

Answer 1

The Visual Studio built in web server can’t handle cross domain connections.

Solution 1: make a new virtual directory for your project and run in IIS
Solution 2: add crossdomain.xml configuration file to your website project containing

<?xml version="1.0"?>
<!DOCTYPE cross-domain-policy SYSTEM
     "http://www.macromedia.com/xml/dtds/cross-domain-policy.dtd">
<cross-domain-policy>  
    <allow-http-request-headers-from domain="*" headers="*"/>
</cross-domain-policy>