ajax Control Toolkit 4.1.40412.0 chart controls cannot be compiled? - asp.net

Question

I'm using Ajax chart(Pie chart, Line chart, bar chart) in my project. All Reference to this ajax is properly. And it worked well in the old version . When I upgrade to ajax Control Toolkit 4.1.40412.0 . I cannot compile my project anymore. The error display:
Warning 2 Element 'PieChart' is not a known element. This can occur if there is a compilation error in the Web site, or the web.config file is missing.
I added in web.config:
<pages validateRequest="false" clientIDMode="AutoID">
<controls>
<add tagPrefix="asp" assembly="AjaxControlToolkit"
namespace="AjaxControlToolkit" />
</controls>
</pages>
and in my HTML form:
<asp:PieChart ID="PieChart1" runat="server" ChartHeight="535" ChartWidth="535"
Visible="true" borderstyle="None" forecolor="White"></asp:PieChart>
What is wrong with this version in my webconfig?
And I also remember to add Reference:
And its property is:

Answer 1

This is because of the tagPrefix="asp". You are actually getting an error
The type or namespace name 'PieChart' does not exist in the namespace 'System.Web.UI.WebControls' (are you missing an assembly reference?)
To make it work, change the tag prefix
web.config
<pages>
<controls>
<add tagPrefix="ajaxToolkit" assembly="AjaxControlToolkit" namespace="AjaxControlToolkit" />
</controls>
</pages>
markup
<asp:ScriptManager ID="ScriptManager1" runat="server"></asp:ScriptManager>
<ajaxToolkit:PieChart ID="PieChart1" runat="server"
ChartHeight="535"
ChartWidth="535"
Visible="true"
BorderStyle="None"
ForeColor="White">
</ajaxToolkit:PieChart>
NuGet Package Link: https://www.nuget.org/packages/AjaxControlToolkit/