尝试:
<ajaxToolkit:CalendarExtender ID="CalendarExtender1" runat="server" TargetControlID="Date1">
</ajaxToolkit:CalendarExtender>
更新:
您的 web.config 中有以下内容吗?
<pages>
<controls>
<add tagPrefix="asp" namespace="System.Web.UI" assembly="System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
<add namespace="AjaxControlToolkit" assembly="AjaxControlToolkit" tagPrefix="asp" />
</controls>
</pages>
<compilation>
<assemblies>
<add assembly="System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
<add assembly="System.Web.Extensions.Design, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
</assemblies>
</compilation>
<httpHandlers>
<remove verb="*" path="*.asmx" />
<add verb="*" path="*.asmx" validate="false" type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
<add verb="*" path="*_AppService.axd" validate="false" type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
<add verb="GET,HEAD" path="ScriptResource.axd" type="System.Web.Handlers.ScriptResourceHandler, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" validate="false" />
</httpHandlers>
<httpModules>
<add name="ScriptModule" type="System.Web.Handlers.ScriptModule, System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
</httpModules>
更新二
将以下内容放在您的 aspx 页面顶部。
<%@ Register Tagprefix="asp" Namespace="AjaxControlToolkit" Assembly="AjaxControlToolkit" %>
另外,您引用的是 AjaxControlToolkit.dll,对吗?它应该在您的 bin 目录中。右键项目,Add Reference菜单选择添加。