Masked Edit Validator always says date is invalid

I have the following code and no matter what I put in the txtStartDate textbox, the validator always says it is an invalid value.  Suggestions?

<asp:TextBox id="txtStartDate" runat="server"
MaxLength="10" TabIndex="9"
ValidationGroup="contentpage"></asp:TextBox>

<Toolkit:MaskedEditExtender ID="metxtStartDate" runat="server"
AutoComplete="False" Mask="99/99/9999"
MaskType="Date" TargetControlID="txtstartdate"
ValidateRequestMode="Enabled"
UserDateFormat="MonthDayYear" PromptCharacter="_" ></Toolkit:MaskedEditExtender>                                                    

<asp:ImageButton ID="ibStartDateCalendar" ImageUrl="~/images/Calendar.gif" runat="server" />

<Toolkit:CalendarExtender ID="calXStartDate" runat="server" TargetControlID="txtStartDate"
PopupButtonID="ibStartDateCalendar" StartDate="01/01/1900" EndDate="12/31/2100"></Toolkit:CalendarExtender>

<Toolkit:MaskedEditValidator ID="mevStartDate" runat="server"                                                        
ControlExtender="metxtStartDate"
ControlToValidate="txtStartDate"
ValidationExpression="^(\d{2})/(\d{2})/(\d{4})$"
IsValidEmpty="false"
EmptyValueMessage="[Start Date] is a required field."
InvalidValueMessage="[Start Date] is an invalid date 1."
EmptyValueBlurredText="(E)"
InvalidValueBlurredMessage="(E)"
Display="Static"
TooltipMessage="[Start Date] is an invalid date 4."
ValidationGroup="contentpage"
ForeColor="Red"/>