I add a ErrorProvider on a form
if (string.IsNullOrEmpty(txtPersonName.Text)) {             
    m_ErrorProvider.SetError(txtPersonName, "Name is incorrect");
} else {

In VS2005, I have a base form that is designed to be inherited by many other
forms in an application.  This base form contains various controls bound to a
dataset (ds1).  The dataset is set to Protected so the base control can have
access to it.  I created an inherited form (call ...

This example has been cut from a larger context, therefore it looks very
simple. It has just been created to illustrate the error. I have overridden
the standard TextBox so it now looks like this:
   public class MyTextBox : System.Windows.Forms.TextBox