How to show WorkerThread exception in textbox ?

This is common error when one starts with WinForms programming.
You need to do something like this:

if (txtBxException.InvokeRequired)
        txtBxException.Invoke(new MethodInvoker(
            delegate
            {
                txtBxException.Text = "Describe error here";
            }
            ));
    else
    {
        txtBxException.Text = "Describe error here";
    }

The problem there is limitation in WinForms that controls can be updated only from main (GUI) thread, on which they were originally created.
So, when you're working on background thread you need to deffer updating control to main thread using .Invoke() or .BeginInvoke() methods.