Enable / Disable and Show / Hide controls outside the Update Panel during AsyncPostBack in ASP.Net

You can not perform actions on controls outside the updatepanel from controls inside update panel.
You need to put your button(on which action is to be performed) in update panel. Necessarily not in the same panel but in other update panel.
then you can add following code(to hide button in updatepanel2) to make it work:

aspx page

<asp:ToolkitScriptManager ID="ToolkitScriptManager1" runat="server">
       </asp:ToolkitScriptManager>
       <asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Always">
           <ContentTemplate>
               <asp:Button ID="Button2" runat="server" onclick="Button2_Click" Text="GO for it" />
           </ContentTemplate>
       </asp:UpdatePanel>
       <br />
       <asp:UpdatePanel ID="UpdatePanel2" runat="server" UpdateMode="Conditional">
       <ContentTemplate>
        <asp:Button ID="Button1" runat="server" Text="Button" />
       </ContentTemplate>
       </asp:UpdatePanel>

code behind:

protected void Button2_Click(object sender, EventArgs e)
    {
        Button1.Visible = false;
        UpdatePanel2.Update();
    }

lemme know if it helps :)