I am having an ajax toolkit calendar extender with the code below:
<asp:TextBox ID="txtStartDate" runat="server" CssClass="textbox" ToolTip="Enter the Start Date"></asp:TextBox>
<asp:Image ImageUrl="/images/cal.gif" runat="server" ID="imgStartDate" ToolTip="Please Pick/Enter a StartDate" />
<ajaxToolkit:CalendarExtender TargetControlID="txtStartDate" PopupButtonID="imgStartDate"
runat="server" ID="CalendarExtender1" PopupPosition="Right" Format="dd/MM/yyyy">
</ajaxToolkit:CalendarExtender>
<asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" ValidationGroup="Submit"
Text="*Start Date is required" ControlToValidate="txtStartDate" Display="Static">
</asp:RequiredFieldValidator>
<asp:RegularExpressionValidator ID="RegularExpressionValidator1" runat="server" ControlToValidate="txtStartDate"
ValidationExpression="(0[1-9]|[12][0-9]|3[01])[- /.](0[1-9]|1[012])[- /.](19|20)\d\d"
ErrorMessage="* Your entry is not a valid Start Date(dd/mm/yyyy)." Display="dynamic"
ValidationGroup="Submit">
</asp:RegularExpressionValidator>
<ajaxToolkit:TextBoxWatermarkExtender ID="TextBoxWatermarkExtender1" runat="server"
TargetControlID="txtStartDate" WatermarkCssClass="watermarked" WatermarkText="Enter the Start Date(dd/mm/yyyy)">
</ajaxToolkit:TextBoxWatermarkExtender>
When I load the page, it displays the following error:
Error: Sys.ArgumentNullException: Value cannot be null
Parameter name: element
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I am proposing a solution to this problem, but bear in mind that it may not be as exactly perfect. Altogether, you can give it a trial.
Value cannot be null.
Try adding the HTML page like this:
<ajaxtoolkit:modalpopupextender ID="MPE" runat="server" TargetControlID="btnShow"PopupControlID="pnlUserControl"/>
<asp:panel ID="pnlUserControl">
<uc1:myusercontrol id="userControl1" runat="server" />
</asp:panel>
And more additions on your user control front.
Maybe something on: protected void page_load.
Cheers!