RegularExpressionValidator not working

hi,
 
i do have the following code-snippet within asp.net 3.5 c# enabled (coming from http://www.java2s.com/Code/ASP/Validation-by-Function/aspRegularExpressionValidatorforemailaddressC.htm):
 
     <asp:RegularExpressionValidator runat="server" id="reqEmail" ControlToValidate="txtEmail"
                 ValidationExpression="\w+([-+.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*"
                 ErrorMessage="- Email-Adresse ung&uuml;ltig" display="Dynamic">
             </asp:RegularExpressionValidator>
...