Custom Validator to replace MaskedEditValidator

I am currently using a maskedEditValidator to do some validation checks in a field, everything works great until I attempt to insert a maximium value.  My current maskededitvalidator looks like this:
<asp:MaskedEditValidator ID="TestStartEdittxtMaskedEditValidator1" runat="server" ControlExtender="TestStartEdittxt_MaskedEditExtender" ControlToValidate="TestStartEdittxt" EmptyValueMessage="You must enter a Date and Time" ErrorMessage="Date and/or Time is Invalid" ForeColor="Black" InvalidValueMessage="Date and/or Time is Invalid" IsValidEmpty="False" MinimumValue="01/01/2010 00:00" MinimumValueMessage="Year must be 2010 or higher" >
When I add the maximium value i ...