ASP.net 4.0执行ChartImg.axd的子请求时出错

Question

我在ASP.net 4.0中编写了这个简单的程序：

Dim x, y
Dim xcircle() As Double = New Double(360) {}
Dim ycircle() As Double = New Double(360) {}
For t = 0 To 360 Step 1
    x = Math.Cos(t * Math.PI / 180)
    y = Math.Sin(t * Math.PI / 180)
    xcircle(t) = x
    ycircle(t) = y
Next t
Chart1.Series("Series1").Points.DataBindXY(xcircle, ycircle)

我一直收到这个错误：

  

System.Web.HttpException：执行ChartImg.axd的子请求时出错。

这是我的web.config：

<appSettings>
    <add key="ChartImageHandler" value="storage=file;timeout=20;" />
  </appSettings>
  <httpHandlers>
    <add path="ChartImg.axd" verb="GET,HEAD,POST" type="System.Web.UI.DataVisualization.Charting.ChartHttpHandler, System.Web.DataVisualization, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" validate="false" />
  </httpHandlers>
<system.webServer>
    <modules runAllManagedModulesForAllRequests="true" />
    <handlers>
      <remove name="ChartImageHandler" />
      <add name="ChartImageHandler" preCondition="integratedMode" verb="GET,HEAD" path="ChartImg.axd" type="System.Web.UI.DataVisualization.Charting.ChartHttpHandler, System.Web.DataVisualization, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />
    </handlers>
  </system.webServer>