create an event handler for the "Validating"event of the textBox1 control.
We will validate the TextBox to ensure that the user has entered a value.

private void textBox1_Validating(object sender,System.ComponentModel.CancelEventArgs e)
{
ValidateName();
}

private bool ValidateName()
{
bool bStatus = true;
if (textBox1.Text == "")
{
errorProvider1.SetError (textBox1,"Please enter value");
bStatus = false;
}
else
errorProvider1.SetError (textBox1,"");
return bStatus;
}