asp:DropDownList Error: 'DropDownList1' has a SelectedValue which is invalid because it does not exist in the list of items

protected void ddSpecialty_PreRender(object sender, EventArgs e)
{
    if (!ddSpecialty.Items.Contains(new ListItem(registration.Specialty)))
        ddSpecialty.Items.Add(registration.Specialty);
    ddSpecialty.SelectedValue = registration.Specialty;
}

ddl.SelectedIndex = ddl.Items.IndexOf(ddl.Items.FindByValue(value));

ddl.DataBound += (o,e) => ddl.SelectedIndex = ddl.Items.IndexOf(ddl.Items.FindByValue(value));

if (ddl.Items.Contains(new ListItem(selectedFacility)))
    ddl.SelectedValue = selectedFacility;