修改三个属性，就可以让错误提示更详细

<SharePoint>
    <SafeMode MaxControls="200" CallStack="true" DirectFileDependencies="10" TotalFileDependencies="50" AllowPageLevelTrace="false">
      <PageParserPaths>
      </PageParserPaths>
    </SafeMode>
    <WebPartLimits MaxZoneParts="50" PropertySize="1048576" />
    <WebPartCache Storage="CacheObject" />

----------------------------------------------------------------------------------

 <httpHandlers>
      <remove verb="GET,HEAD,POST" path="*" />
      <add verb="GET,HEAD,POST" path="*" type="Microsoft.SharePoint.ApplicationRuntime.SPHttpHandler, Microsoft.SharePoint, Version=12.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" />
      <add verb="OPTIONS,PROPFIND,PUT,LOCK,UNLOCK,MOVE,COPY,GETLIB,PROPPATCH,MKCOL,DELETE,(GETSOURCE),(HEADSOURCE),(POSTSOURCE)" path="*" type="Microsoft.SharePoint.ApplicationRuntime.SPHttpHandler, Microsoft.SharePoint, Version=12.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" />
      <add verb="*" path="Reserved.ReportViewerWebControl.axd" type="Microsoft.Reporting.WebForms.HttpHandler, Microsoft.ReportViewer.WebForms, Version=8.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" />
      <add verb="GET" path="*.json" type="WebApplication.AjaxHandler, WebApplication , Version=1.0.0.0, Culture=neutral, PublicKeyToken=96a6263d31b4ccbc" />
    </httpHandlers>
    <customErrors mode="Off" />
    <httpRuntime maxRequestLength="51200" />
    <authentication mode="Windows" />

---------------------------------------------------------------------------------------

 <compilation batch="false" debug="false">
      <assemblies>
        <add assembly="Microsoft.SharePoint, Version=12.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" />
      </assemblies>