I have the following situation: I have a textbox inside an ajax updatepanel. Wherever the user types in the textbox I must display a message (different message that depends on the user typed data).

     <asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Always">
        <ContentTemplate>
            <asp:TextBox ID="txtMyTexbox" runat="server" Width="500px" OnTextChanged="txtMyTexbox_TextChanged" AutoPostBack="true"></asp:TextBox>
            <br />
            <asp:Label ID="lblMessage" runat="server" CssClass="errorMessage" Visible="false">Hello World</asp:Label>
         </ContentTemplate>
            <Triggers>
             <asp:AsyncPostBackTrigger ControlID="txtMyTexbox" />
            </Triggers>
      </asp:UpdatePanel>

In server side I have written the following at page load

ScriptManager.GetCurrent(this).RegisterAsyncPostBackControl(txtMyTexbox);

and the method like this

protected void txtMyTexbox_TextChanged(object sender, EventArgs e)
    {           
            if (.....)
            {
                lblMessage.Visible = false;
            }
            else
            {
                lblMessage.Visible = true;
            }            
    }

My problem now is that: when the user types in the textbox it doesn't cause OnTextChanged event.

Am I missing something?