Form Not Refreshing

Hi All,
 
I am searching for a customer and displaying results on the same form. Now for some reason even If I am searching using correct format of the data the system is showing some predefined error messages. This measn that my previous error message is not refreshing.
This is the code:
 
if (txtANumber.Text.Length == 0 && txtBNumber.Text.Length == 0 && txtCNumber.Text.Length == 0 && txtDNumber.Text.Length == 0 && txtLastName.Text.Length == 0 && txtFirstName.Text.Length == 0 && txtDOB.Text.Length == 0)
        {
            GridViewCustomers.DataSource = null;
            GridViewCustomers.DataBind();
            lblNoResultsMsg.Text = "Please enter search details";
             ...