.NET Ajax工具包HtmlEditorExtender未显示底部工具栏

我对Microsoft.Net Ajax工具包HtmlEditorExtender控件有一个小问题。我遇到的问题是底部工具栏（可以进入html视图模式的工具栏）没有显示，只有文本框上方的顶部工具栏。这是.net 3.5版本。问题是我该如何显示底部工具栏，或者我做错了什么。请参阅下面的代码。

    <%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="ajax" %>
<asp:TextBox ID="txbMessage" runat="server" Width="95%" 
                                    TextMode="MultiLine" Height="156px"></asp:TextBox>
                                    <ajax:HtmlEditorExtender 
                                        ID="htmlEditorExtender1" 
                                        TargetControlID="txbMessage"                                          
                                        runat="server" >
                                        <Toolbar> 
                                                <ajax:Undo />
                                                <ajax:Redo />
                                                <ajax:Bold />
                                                <ajax:Italic />
                                                <ajax:Underline />
                                                <ajax:StrikeThrough />
                                                <ajax:Subscript />
                                                <ajax:Superscript />
                                                <ajax:JustifyLeft />
                                                <ajax:JustifyCenter />
                                                <ajax:JustifyRight />
                                                <ajax:JustifyFull />
                                                <ajax:InsertOrderedList />
                                                <ajax:InsertUnorderedList />
                                                <ajax:CreateLink />
                                                <ajax:UnLink />
                                                <ajax:RemoveFormat />
                                                <ajax:SelectAll />
                                                <ajax:UnSelect />
                                                <ajax:Delete />
                                                <ajax:Cut />
                                                <ajax:Copy />
                                                <ajax:Paste />
                                                <ajax:BackgroundColorSelector />
                                                <ajax:ForeColorSelector />
                                                <ajax:FontNameSelector />
                                                <ajax:FontSizeSelector />
                                                <ajax:Indent />
                                                <ajax:Outdent />
                                                <ajax:InsertHorizontalRule />
                                                <ajax:HorizontalSeparator />                                                
                                                <%--<ajax:InsertImage />--%>
                                            </Toolbar>            
                                    </ajax:HtmlEditorExtender>

<ajax:ToolkitScriptManager ID="ToolkitScriptManager1" runat="server"></ajax:ToolkitScriptManager>