System.UnauthorizedAccessException: Invalid cross-thread access error

[admin]

 hello,
           i'm getting this error when i'm trying to bind data dynamically from a textbox control to a method,
here is the code...
  private void btn1_click(object sender, routedeventargs e)        {            httpwebrequest request = (httpwebrequest)webrequest.create(new uri("http://postbox.instasecure.com/service/soap/"));            request.method = "post";            request.contenttype = "application/json";            request.begingetrequeststream(new asynccallback(createtagrequesthandler), request);        }
 void createtagrequesthandler(iasyncresult asyncresult)        {            httpwebrequest request = (httpwebrequest)asyncresult.asyncstate;           //getting that error near s...          string s = createtagxml(txtname.text.trim(),txtcolor.text.trim());            streamwriter postdatawriter = new streamwriter(request.endgetrequeststream(asyncresult));            postdatawriter.write(s, 0, s.length);            postdatawriter.flush();            postdatawriter.close();            request.begingetresponse(new asynccallback(createtagresponsehandler), request);        }
 thanx in advance,
hari