ASP.Net: Ajax registration question - asp.net

Question

I worked with: ASP.Net: Ajax check for registration as a user?
It has a few errors, I don't understand:
1) It worked only one time for one textbox. If the textbox is edited a second time, the breakpoint will not be hited. Why?
2) For my Email, I have a check, that there is no duplicate, when there is one, there should the set an error panel visible, but it don't show.
protected void txtEMail_TextChanged(object sender, EventArgs e)
{
Business.UserHandling uh = new Business.UserHandling();
if (uh.CheckIfEmailExists(txtEMail.Text))
{
panelHelp.Visible = true;
lblHelp.Text = "EMail existriert schon.";
}
}

Answer 1

When the update mode is conditional
<asp:scriptmanager runat="server" id="sm1" />
<asp:updatepanel runat="server" id="up1" updatemode="Conditional"> // here the updatemode is conditional ...
<contenttemplate>
<asp:textbox runat="server" id="tbUsername" autopostback="true" ontextchanged="tbUsername_TextChanged" />
<asp:customvalidator runat="server" text="Email already used" id="cusValEmail" />
<asp:textbox runat="server" id="tbPassword" />
</contenttemplate>
</asp:updatepanel>
You need to call
protected void txtEMail_TextChanged(object sender, EventArgs e)
{
Business.UserHandling uh = new Business.UserHandling();
if (uh.CheckIfEmailExists(txtEMail.Text))
{
panelHelp.Visible = true;
lblHelp.Text = "EMail existriert schon.";
}
up1.Update(); // call to update the update panel "up1"
}
Sorry I'm a bit rusty, it's a while since I've used update panels.

Answer 2

After an update panel updates you must reinitialise the javascript on the html elements inside it.
So, to the end of your method you could add:
protected void txtEMail_TextChanged(object sender, EventArgs e)
{
Business.UserHandling uh = new Business.UserHandling();
if (uh.CheckIfEmailExists(txtEMail.Text))
{
panelHelp.Visible = true;
lblHelp.Text = "EMail existriert schon.";
}
// Re-init javascript
ScriptManager.RegisterStartupScript(Type, String, "add onchange js here", Boolean);
}
see http://msdn.microsoft.com/en-us/library/system.web.ui.clientscriptmanager.registerstartupscript.aspx