Date validation for a textbox

Question

I have been using this to take date as mm/dd/yyyy format...

Answer 1

You might want to use a regular expression for the date :

<asp:RegularExpressionValidator ID="dateValRegex" runat="server" ControlToValidate="txtDob" ErrorMessage="Please Enter a valid date in the format (mm/dd/yyyy)" ValidationExpression="^(0[1-9]|1[012])[- /.](0[1-9]|[12][0-9]|3[01])[- /.](19|20)\d\d$"></asp:RegularExpressionValidator>

Also, as Daniel pointed out below you will need to use this in conjunction with your other validators to fully validate the date.