Funzione se TUTTI i textbox NON SONO VUOTI. Se invece ce n'è anche solo uno già vuoto, non ne cancella nessuno e si attiva il controllo di validazione su quello vuoto. Perché?

Riporto per intero il codice così se volete potete provare voi stessi...

<%@ Page Language="VB" %>
<%@ import Namespace="System.Data" %>
<%@ import Namespace="System.Data.OleDb" %>


<script runat="server">

sub Submit(obj as object, e as eventargs)
...
end sub


sub Cancella_Form(obj as object, e as eventargs)
tbNome.text = ""
tbCognome.text = ""
tbGiornoNascita.text = ""
tbMeseNascita.text = ""
tbAnnoNascita.text = ""
tbUsername.text = ""
tbPassword.text = ""
tbPassword2.text = ""
end sub
</script>

<html>
<head>
<title>giulioferri.it - Registrazione</title>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
</head>

<body background="bg.gif" text="#FFFFFF" link="#FFFF00" vlink="#FFCC00">
<div align="center">
<p align="center"><font size="6" face="Georgia, Times New Roman, Times, serif">Registrazione</font></p>


<font color="#FFCC00" size="3" face="Georgia">giulioferri.it</font></p>


</p>
<form runat="server">
<table width="394" border="0" cellpadding="2" cellspacing="2" background="bg_giallo.gif">
<tr background="bg.gif">
<td colspan="2" background="bg.gif"><div align="center"><font color="#FFFFFF" size="5" face="Georgia, Times New Roman, Times, serif">Inserimento
Dati</font></div></td>
</tr>
<tr>
<td width="36%"><font color="#000000" size="2" face="Georgia, Times New Roman, Times, serif">Nome</font></td>
<td width="64%"><div align="left">
<asp:textbox ID="tbNome" Width="150" runat="server" />
<font color="#CC0000" size="2" face="Georgia, Times New Roman, Times, serif">


<font size="1">
<asp:requiredfieldvalidator runat="server"
controltovalidate="tbNome"
errormessage="Inserire il NOME"/>
</font> </font></div></td>
</tr>
<tr>
<td><font color="#000000" size="2" face="Georgia, Times New Roman, Times, serif">Cognome</font></td>
<td><div align="left">
<asp:textbox ID="tbCognome" Width="150" runat="server" />
<font color="#CC0000" size="2" face="Georgia, Times New Roman, Times, serif">


<font size="1">
<asp:requiredfieldvalidator runat="server"
controltovalidate="tbCognome"
errormessage="Inserire il COGNOME"/>
</font> </font></div></td>
</tr>
<tr>
<td height="31"><font color="#000000" size="2" face="Georgia, Times New Roman, Times, serif">Data
di nascita<font color="#FF0000" size="1"> </font></font><font color="#000000" size="2" face="Georgia, Times New Roman, Times, serif"><font color="#FF0000" size="1">(opz.)</font></font></td>
<td><div align="left">
<asp:textbox ID="tbGiornoNascita" Width="30" runat="server" />
<font color="#000000" size="3" face="Georgia, Times New Roman, Times, serif">/</font>
<asp:textbox ID="tbMeseNascita" Width="30" runat="server" />
<font color="#000000" size="3" face="Georgia, Times New Roman, Times, serif">/</font>
<asp:textbox ID="tbAnnoNascita" Width="60" runat="server" />
<font color="#666666" size="1" face="Georgia, Times New Roman, Times, serif">(Es:
04/05/1976)</font><font color="#666666" size="2" face="Georgia, Times New Roman, Times, serif">

</font></div></td>
</tr>
<tr>
<td></td>
<td><div align="left"></div></td>
</tr>
<tr>
<td><font color="#000000" size="2" face="Georgia, Times New Roman, Times, serif">
USERNAME</font></td>
<td><div align="left">
<asp:textbox ID="tbUsername" Width="150" runat="server" />
<font color="#666666" size="1" face="Georgia, Times New Roman, Times, serif">@giulioferri.it</font>

<font color="#CC0000" size="1" face="Georgia, Times New Roman, Times, serif">

<asp:requiredfieldvalidator runat="server"
controltovalidate="tbUsername"
errormessage="Inserire uno USERNAME"/>
</font></div></td>
</tr>
<tr>
<td height="39"><font color="#000000" size="2" face="Georgia, Times New Roman, Times, serif">
PASSWORD</font></td>
<td><div align="left">
<asp:textbox ID="tbPassword" TextMode="Password" Width="150" runat="server" />
<font color="#CC0000" size="2" face="Georgia, Times New Roman, Times, serif">


<font size="1">
<asp:requiredfieldvalidator runat="server"
controltovalidate="tbPassword"
errormessage="Inserire una PASSWORD"/>
</font> </font></div></td>
</tr>
<tr>
<td><font color="#000000" size="2" face="Georgia, Times New Roman, Times, serif">Ripeti
PASSWORD </font></td>
<td><div align="left">
<asp:textbox ID="tbPassword2" TextMode="Password" Width="150" runat="server" />
<font color="#CC0000" size="2" face="Georgia, Times New Roman, Times, serif">


<font size="1">
<asp:requiredfieldvalidator runat="server"
controltovalidate="tbPassword2"
errormessage="Ripetere la PASSWORD"/>
</font> </font></div></td>
</tr>
<tr>
<td></td>
<td><div align="left"></div></td>
</tr>
</table>


<asp:button ID="bInvia" Text="Invia" OnClick="Submit" runat="server" /><asp:button ID="bCancella" Text="Cancella" OnClick="Cancella_Form" runat="server" /></p>
</form>


</p>
</div>
</body>
</html>