ControlToValidate weird problem

The code below is commented out in my code but it still causes an error - Line: 488 Error: Unable to set property 'controltovalidate' of undefined or null reference -
at runtime, then everything works ok. If I remove it completely then my submit button doesn't submit anymore. If I put it back in, but still commented out, my submit button works again.
<!-- <asp:RequiredFieldValidator ID="RequiredFieldValidatorNationality" runat="server" ErrorMessage="Please select a Nationality" ForeColor="Red" InitialValue="-1" ControlToValidate="ddlNationality"></asp:Requir ...