<%@ Register Assembly="AsyncControls" Namespace="DelvingWare.AsyncControls" TagPrefix="dw" %>

<dw:AsyncPanel runat="server" ID="pnlMain" CssClass="asyncPanel">
    
    <p>
        <dw:AsyncButton runat="server" ID="btShowPanel" 
        Text="Show Nested AsyncPanel" 
        OnClick="btShowPanel_Click" 
        DisableDuringCallback="false" 
        CssClass="greyButton"/>
        <br />
        <br/>
        <dw:AsyncButton runat="server" ID="btHidePanel" 
        Enabled="false" 
        Text="Hide Nested AsyncPanel" 
        OnClick="btHidePanel_Click" 
        DisableDuringCallback="false" 
        CssClass="greyButton"/>
        <p/>
        <dw:AsyncPanel runat="server" ID="pnlNestedMain" 
        Visible="false"            
        CssClass="nestedPanel">
            <div class="nestedPanelText">I'm inside a nest AsyncPanel</div>
        </dw:AsyncPanel>
    </p>
    
</dw:AsyncPanel>

using System;
using DelvingWare.AsyncControls;
...
protected void btShowPanel_Click( object sender, AsyncEventArgs ae )
{
    // show the AsyncPanel
    pnlNestedMain.Visible = true;

    // disable/enable the AsyncButtons
    btHidePanel.Enabled = true;
    btShowPanel.Enabled = false;
}

protected void btHidePanel_Click( object sender, AsyncEventArgs ae )
{
    // hide the AsyncPanel
    pnlNestedMain.Visible = false;

    // disable/enable the AsyncButtons
    btShowPanel.Enabled = true;
    btHidePanel.Enabled = false;
}

Imports System
Imports DelvingWare.AsyncControls
...

Protected Sub btShowPanel_Click(ByVal sender As Object, ByVal ae As AsyncEventArgs)
    ' show the AsyncPanel
    pnlNestedMain.Visible = true
    ' disable/enable the AsyncButtons
    btHidePanel.Enabled = true
    btShowPanel.Enabled = false
End Sub

Protected Sub btHidePanel_Click(ByVal sender As Object, ByVal ae As AsyncEventArgs)
    ' hide the AsyncPanel
    pnlNestedMain.Visible = false
    ' disable/enable the AsyncButtons
    btShowPanel.Enabled = true
    btHidePanel.Enabled = false
End Sub

.asyncPanel 

{
    padding: .5em;
    width: 90%;
    border: 1px solid #ddd;
    background-color: white;
    font-family: Verdana, Arial, Serif;
    font-size: 10pt;
}
.nestedPanel 

{
}
.nestedPanelText 

{
    background-color: #ddd;
    border: 1px solid #777;
    padding-left: 20px;
}