ajaxcontroltoolkit - ASP.NET - Ajax Control Toolkit - TabContainer always hidden -

I used the following code to add tabontaneousear to the page

   Asp: TabContainer ID = "TabContainer1" runat = "server" & gt; & Lt; Asp: TabPanel runat = "server" headertax = "tab one" id = "tab panel 0" & gt; & Lt; ContentTemplate & gt; & Lt; ASP: Text Box ID = "Text Box 1" Runat = "Server" & gt; & Lt; / Asp: text box & gt; & Lt; / ContentTemplate & gt; & Lt; / ASP: TabPanel & gt; & Lt; Asp: TabPanel runat = "server" headertax = "tab two" id = "tabpel 1" & gt; & Lt; ContentTemplate & gt; & Lt; ASP: Button ID = "Button 1" Runat = "Server" Text = "Button" /> & Lt; / ContentTemplate & gt; & Lt; / ASP: TabPanel & gt; & Lt; / ASP: TabContainer & gt;   
 But when the page is presented, the tabpellel is always hidden, I added the HTML code via firebug and found that the visibility is hidden ... What is the problem?   
 
 
 Did you try to set ActiveTab-property (with codebehind) or ActiveBabIndex with codebehind or aspx is?  
  ActiveTabIndex = "0" style = "display: block; visibility: visible;"  
 You can also see if it works if you explicitly set the display in the view:   
 Are you sure that Ajax libraries Has been loaded correctly? Do you have other Ajax controls inside your tabontanear? Check that all of your HTML is valid on that page.  
 Are you using the latest Ajax Toolkit and ToolmatScript Manager instead of Script Manager?