System.Windows.Threading Namespace provides classes that support the Silverlight threading system.
Dispatcher Class provides services for managing the queue of work items for a thread.
Dispatcher.BeginInvoke Method (Action) executes the specified delegate asynchronously on the thread the Dispatcher is associated with.
E.g.
Dispatcher.BeginInvoke(() => { MessageBox.Show("Member Number does not exist in the system."); this.memberNumberTextBox.Text = string.Empty; this.memberNumberTextBox.Focus(); });