Masked Edit Validator making the wrong validation

Hi, 

I have the above wrongly validating an entered date WHEN the 'day' part of the day is greater than 12; so for example: 

07/03/2012 validates is ok; 

13/03/2012 is validated is 'Invalid'. 

It is as if the validator is thinking that the day part is the month and that month part is the day. 

My Mask is 99/99/9999 and the date format is dd/MM/yyyy (on the calendar). 

here is the code: 

<tr>
<td>
Date Due: *
</td>
<td>
<asp:TextBox ID="txtDateDue" runat="server" Width="110"></asp:TextBox>
<ajaxToolkit:CalendarExtender ID="txtDateDue_CalendarExtender" Format="dd/MM/yyyy" runat="server" Enabled="True" PopupButtonID="txtDateDue" TargetControlID="txtDateDue">
</ajaxToolkit:CalendarExtender>
</td>
<td>
<ajaxToolkit:MaskedEditExtender ID="meDateDue"
runat="server"
TargetControlID="txtDateDue"
Mask="99/99/9999"
MaskType="Date" CultureName=""
MessageValidatorTip="true" />
<ajaxToolkit:MaskedEditValidator ID="mvDateDue"
runat="server"
ControlToValidate="txtDateDue"
ControlExtender="meDateDue"
Display="Dynamic" ValidationGroup="valGroupInsert"
IsValidEmpty="true"
EmptyValueMessage="A Date is Required"
InvalidValueMessage="Invalid." />
<asp:RequiredFieldValidator ID="valDateDue" ControlToValidate="txtDateDue" ValidationGroup="valGroupInsert" InitialValue="" runat="server" Display="Dynamic" ErrorMessage="Required."></asp:RequiredFieldValidator>
</td>
</tr>

Could you please suggest a solution for this problem.. 

Thank you .