Hi Mugil,
Here is an sample. Please compare it with yours.
<%@ Page Language="C#" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<script runat="server">
protected void TabContainer1_ActiveTabChanged(object sender, EventArgs e)
{
}
</script>
<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
<title>Untitled Page</title>
</head>
<body>
<form id="form1" runat="server">
<asp:ScriptManager ID="ScriptManager1" runat="server">
</asp:ScriptManager>
<ajaxToolkit:TabContainer ID="TabContainer1" runat="server" AutoPostBack="true" OnActiveTabChanged="TabContainer1_ActiveTabChanged">
<ajaxToolkit:TabPanel ID="TabPanel1" runat="server">
<HeaderTemplate>
Tab1</HeaderTemplate>
<ContentTemplate>
<asp:Panel ID="Panel1" runat="server">
<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
</asp:Panel>
</ContentTemplate>
</ajaxToolkit:TabPanel>
<ajaxToolkit:TabPanel ID="TabPanel2" runat="server" >
<HeaderTemplate>
Tab2</HeaderTemplate>
<ContentTemplate>
<asp:Panel ID="Panel2" runat="server" Height="200" Width="100%" style="overflow:auto">
<br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br>
<asp:TextBox ID="TextBox2" runat="server"></asp:TextBox>
</asp:Panel>
</ContentTemplate>
</ajaxToolkit:TabPanel>
</ajaxToolkit:TabContainer>
</form>
</body>
</html>
If it doesn't work, please check your system environments. We suggest that you should upgrade your Ajax Control Toolkit to the latest version. (10618 or 10920).
Hope this helps.
Best regards,
Jonathan.