tabcontainer problem

this is my tab container
<cc1:TabContainer ID="TabContainer1" runat="server" ActiveTabIndex="0">
<cc1:TabPanel runat="server" HeaderText="TabPanel1" ID="TabPanel1">
<ContentTemplate><asp:Button ID="Button1" runat="server" Text="Button" /></ContentTemplate>
</cc1:TabPanel>

<cc1:TabPanel ID="TabPanel2" runat="server" HeaderText="TabPanel2" Enabled="False">
<ContentTemplate >
<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
</ContentTemplate>
</cc1:TabPanel>
<cc1:TabPanel ID="TabPanel3" runat="server" HeaderText="TabPanel3"></cc1:TabPanel>
</cc1:TabContainer>

now I'm enabling "TabPanel2" from code behind

Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
'TabPanel2.Enabled = True
'TabContainer1.ActiveTabIndex = 1
End Sub

while clicking the button its showing this error

Microsoft JScript runtime error: Sys.InvalidOperationException: Handler was not added through the Sys.UI.DomEvent.addHandler method.

How to solve this?