Security error on web request

e.Error    {System.Security.SecurityException: Security error.
   at MS.Internal.InternalWebRequest.Send()
   at System.Net.BrowserHttpWebRequest.BeginGetResponseImplementation()
   at System.Net.BrowserHttpWebRequest.InternalBeginGetResponse(AsyncCallback callback, Object state)
   at System.Net.AsyncHelper.BeginOnUI(BeginMethod beginMethod, AsyncCallback callback, Object state)
   at System.Net.BrowserHttpWebRequest.BeginGetResponse(AsyncCallback callback, Object state)
   at System.Net.WebClient.DownloadBits(WebRequest request, Stream writeStream, CompletionDelegate completionDelegate, AsyncOperation asyncOp)
   at System.Net.WebClient.DownloadStringAsync(Uri address, Object userToken)}    System.Exception {System.Security.SecurityException}

 
This is for a REST API.  It only does it certain times.  I've made t ...