I used the following code to add TabContainer to page
<asp:TabContainer ID="TabContainer1" runat="server">
<asp:TabPanel runat="server" HeaderText="tab one" ID="TabPanel0">
<ContentTemplate>
<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
</ContentTemplate>
</asp:TabPanel>
<asp:TabPanel runat="server" HeaderText="tab two" ID="TabPanel1">
<ContentTemplate>
<asp:Button ID="Button1" runat="server" Text="Button" />
</ContentTemplate>
</asp:TabPanel>
</asp:TabContainer>
but when the page is rendered TabPanel is always Hidden,I wateched the html code by Firebug and found visibility is hidden... what is the problem? http://i.stack.imgur.com/m1eSW.jpg
Have you tried to set the ActiveTab-Property(from codebehind) or the ActiveTabIndex from codebehind or aspx?
You could also check if it works if you explicitly set the display to visible:
ActiveTabIndex="0" style="display:block;visibility:visible;"
Are you sure that the Ajax libraries are loaded correctly? Do you have other Ajax-Controls inside of your TabContainer? Check if all of your html in that page is valid.
Are you using the latest AjaxToolkit and the ToolkitScriptManager instead of the ScriptManger?