validationsummary duplicates errors

[Netwhiz]

I have a problem using the ValidationSummary control in a C#
application. when a
RequiredFieldValidator error occurs, it is displayed twice in the
ValidationSummary control

i.e. * Enter Code
* Enter Code

A search on the error message (and control name) reveals only one
RequiredFieldValidator which can raise the error condition.

Code:
<asp:validationsummary id="ValidSummary" CssClass="NormalRed"
Runat="server" EnableClientScript="False" />
..
..
<asp:RequiredFieldValidator ID="Req1" ControlToValidate="CourseCode"
ErrorMessage="Enter Course Code" Runat="server"
EnableClientScript="False" />

Can anyone suggest something to try?