Exception Invalid Cross Thread Access While assigning Values to Textbox.

Hello Experts i am developing a silverlight application and deploying in CRM Online. The application is about querying some records using SOAP service and storing it to an ObservableCollection List. From this list i  am assigning the values to Texboxes but everytime i am getting Invalid Cross thread Access Exception. I am doing as below.

if(personalDetails.Count>0)

{

 this.Dispatcher.BeginInvoke(() => txtTelephone.Text = (Convert.ToString(Convert.ToDouble(personalDetails[index].telephone))));
                        this.Dispatcher.BeginInvoke(() => txtCity.Text =(Convert.ToString(Convert.ToDouble(personalDetails[index].City))));
                        this.Dispatcher.BeginInvoke(() => txtDistance.Text = Convert.ToString(Convert.ToDouble(personalDetails[index].Distance).ToString("0.00")));

}

where  i am wrong.

Please suggest

Thank you

saroj