Mask Edit and MASK edit Validator :Error :StartIndex cannot be less than zero. Parameter name: startIndex

<cc1:MaskedEditExtender ID="MaskedEditExtender1" runat="server" masktype="DateTime" Targetcontrolid="Txtdate" AcceptAMPM ="true" Mask ="  /  /    "
 InputDirection ="LeftToRight" ErrorTooltipEnabled="true" MessageValidatorTip ="true"   ></cc1:MaskedEditExtender><cc1:MaskedEditValidator ID="MaskedEditValidator1" runat="server" ControlToValidate ="Txtdate"  ControlExtender ="MaskedEditExtender1" EmptyValueBlurredText ="*"
InvalidValueBlurredMessage ="!"  EmptyValueMessage ="Date and Time is requeried"
 InvalidValueMessage ="Date and time is invalid" IsValidEmpty ="true"
TooltipMessage ="Input Date and Time : 10/9/2011/ 10:12:30 AM" ></cc1:MaskedEditValidator>

Why show this error