Hola !
Mira esto es lo que tengo en mi codigo:
<asp:TemplateField HeaderText="alta">
<ItemStyle wrap="False"></ItemStyle>
<ItemTemplate>
<asp:Label ID="lblBirthDate" runat="server" Text='<%# DataBinder.Eval(Container.DataItem, "alta") %>' />
</ItemTemplate>
<EditItemTemplate>
<cc1:UltimateDatePicker id="UltimateDatePicker1" runat="server" dateformat="dd/MM/yyyy">
<DatePickerTextBox width="80px" height="19px" text='<%# DataBinder.Eval(Container.DataItem, "alta") %>'>
</DatePickerTextBox>
</cc1:UltimateDatePicker>
<cc1:UltimateCalendar id="UltimateCalendar1" runat="server" font-size="8pt" font-names="Verdana" daynameformat="FirstTwoLetters"
nextmonthtext="<img border='0' src='~/imagenes/calendario_next.png'>"
prevmonthtext="<img border='0' src='~/imagenes/calendario_previous.png'>"
initiallyhidden="True" autopostbackonselectionchanged="False">
<DayStyle backcolor="AliceBlue"></DayStyle>
<OtherMonthDayStyle forecolor="Gray"></OtherMonthDayStyle>
<DayHeaderStyle backcolor="LightSkyBlue"></DayHeaderStyle>
<TitleStyle wrap="False" forecolor="White" backcolor="RoyalBlue"></TitleStyle>
<DayOverStyle backcolor="Orange"></DayOverStyle>
<SelectorStyle forecolor="Red"></SelectorStyle>
<MultiMonthTitleStyle wrap="False"></MultiMonthTitleStyle>
<TodayDayStyle forecolor="White" backcolor="RoyalBlue"></TodayDayStyle>
</cc1:UltimateCalendar>
</EditItemTemplate>
</asp:TemplateField>