VB NET user control panel doesn't show up - vb.net

Question

I'm not a vb net master, and I got some problem I still can't solve.
I have a main page, when I click on a button I want to display a panel (a web user control I imported in the main page) but it shows nothing.
I think I've done some stupid mistake but I can't get out of it.
Let me show you some code:
This is the user control:
<asp:Panel ID="MainPanelUserMessage" runat="server" Height="278px" Style="z-index: 100; left: 0px;
position: absolute; top: 0px; background-position: center center; background-attachment: fixed; background-repeat: repeat; font-size: 12px; font-family: Tahoma;" Width="746px">
<asp:Label ID="LabelTitoloMex" runat="server" Style="font-weight: bold; font-size: 14px;
z-index: 100; left: 0px; color: #ffffff; font-family: Verdana, Tahoma; position: absolute;
top: 0px; background-color: #000000; text-align: center" Text="Messaggio dal supporto tecnico"
Width="746px"></asp:Label>
<asp:Label ID="LabelOggettoMex" runat="server" Style="font-weight: bold; font-size: 12px;
z-index: 105; left: 7px; color: #424242; font-family: Tahoma, Verdana; position: absolute;
top: 30px" Text="Oggetto:"></asp:Label>
<asp:TextBox ID="TextOggettoUser" runat="server" MaxLength="100" Style="font-size: 12px;
z-index: 106; left: 68px; font-family: Tahoma, Verdana; position: absolute; top: 30px;
text-align: left" ToolTip="Oggetto" Width="660px" ReadOnly="True"></asp:TextBox>
<asp:TextBox ID="TextMessaggioUser" runat="server" Height="160px" MaxLength="2000" Style="font-size: 12px;
z-index: 107; left: 9px; font-family: Tahoma, Verdana; position: absolute; top: 60px;
text-align: left" TextMode="MultiLine" ToolTip="Messaggio" Width="721px"
ReadOnly="True"></asp:TextBox>
<asp:Button ID="okButton" runat="server" Style="font-size: 12px;
font-family: Tahoma, Verdana; text-align: left" CssClass="style1"
Text="Chiudi"> </asp:Button>
<input id="cbxRemember" type="checkbox" class="style2" />
<asp:Label ID="lblRemember" runat="server" Style="font-weight: bold; font-size: 12px;
color: #424242; font-family: Tahoma, Verdana; "
Text="Non mostrare più questo messaggio." CssClass="style3"></asp:Label>
</asp:Panel>
In the page it will contain the panel it autogenerated this:
Protected WithEvents MessaggioUtente1 As Global.System.Web.UI.WebControls.Panel
When i click the button this is the code that is executed:
PanelClientEnabled = False //this works and obfuscates background
UserMessage1.Visible = True
But the panel doesn't show up.
Any hint?