AjaxControlToolkit.TabContainer chklstFSOptions = this.Page.FindControl("tbcontainer") as AjaxControlToolkit.TabContainer;
I was TabContainer in GeneratePackage.aspx as below
HTML-
<ajx:TabContainer ID="tbcontainer" runat="server" ActiveTabIndex="0" Width="100%" CssClass="fancy fancy-green" AutoPostBack="true" OnActiveTabChanged="tbcontainer_ActiveTabChanged">
And Access this in ControlCompanyMaster.ascx on button click
HTML-
<asp:Button ID="btnSave" runat="server" Text="Submit" ValidationGroup="save" OnClick="btnSave_Click" OnClientClick="StartProgressBar();" CssClass="btn" Style="float: left; margin-left: 500px; margin-top: 5px;" />
c#
protected void btnSave_Click(object sender, EventArgs e) {
AjaxControlToolkit.TabContainer chklstFSOptions = this.Page.FindControl("tbcontainer") as AjaxControlToolkit.TabContainer;
}