Ho un problema :

Cercando di modificare un campo sul database, mi da questo errore

Microsoft JET Database Engine error '80004005'

Il campo "tabella.TELEFONO" non può contenere una stringa di lunghezza zero.

/edit-process.asp, line 8

questo è il codice di edit.asp :

<%
Dim cod
cod=Request.Querystring("cod")
Dim SQL,Rec
SQL="SELECT * FROM tabella WHERE id="&cod
Set objRs = Server.CreateObject("ADODB.Recordset")
Set objRs=objCn.Execute(SQL)
%>
<div align="center">
<center>
<form method="post" action="edit-process.asp?cod=<%=cod%>">
<table border="0" cellpadding="4" width="400" bgcolor="#000000" cellspacing="1" height="142">
<tr>
<td width="199" bgcolor="#FFFFCC" height="35"><font size="2" face="Verdana">Nome</font></td>
<td width="199" bgcolor="#FFFFCC" height="35">
<p align="center"><input name="nome" maxlength="50" size="25" value="<%=objRs("nome")%>"></td>
</tr>
<tr>
<td width="199" bgcolor="#FFFFCC" height="35"><font size="2" face="Verdana">Indirizzo</font></td>
</center>
<td width="199" bgcolor="#FFFFCC" height="35">
<p align="center"><input name="cognome" maxlength="50" size="25" value="<%=objRs("Indirizzo")%>"></td>
</tr>
<center>
<tr>
<td width="199" bgcolor="#FFFFCC" height="36"><font size="2" face="Verdana">Telefono</font></td>
<td width="199" bgcolor="#FFFFCC" height="36">
<p align="center"><input name="residenza" maxlength="50" size="25" value="<%=objRs("Telefono")%>"></td>
</tr>
<tr>
<tr>
<td width="199" bgcolor="#FFFFCC" height="36"><font size="2" face="Verdana">Fax</font></td>
<td width="199" bgcolor="#FFFFCC" height="36">
<p align="center"><input name="residenza" maxlength="50" size="25" value="<%=objRs("Fax")%>"></td>
</tr>
<tr>
<tr>
<td width="199" bgcolor="#FFFFCC" height="36"><font size="2" face="Verdana">Comune</font></td>
<td width="199" bgcolor="#FFFFCC" height="36">
<p align="center"><input name="residenza" maxlength="50" size="25" value="<%=objRs("Comune")%>"></td>
</tr>
<tr>
<tr>
<td width="199" bgcolor="#FFFFCC" height="36"><font size="2" face="Verdana">Provincia</font></td>
<td width="199" bgcolor="#FFFFCC" height="36">
<p align="center"><input name="residenza" maxlength="50" size="25" value="<%=objRs("Provincia")%>"></td>
</tr>
<tr>
<tr>
<td width="199" bgcolor="#FFFFCC" height="36"><font size="2" face="Verdana">Categoria</font></td>
<td width="199" bgcolor="#FFFFCC" height="36">
<p align="center"><input name="residenza" maxlength="50" size="25" value="<%=objRs("Categoria")%>"></td>
</tr>
<tr>
<tr>
<td width="199" bgcolor="#FFFFCC" height="36"><font size="2" face="Verdana">Figura</font></td>
<td width="199" bgcolor="#FFFFCC" height="36">
<p align="center"><input name="residenza" maxlength="50" size="25" value="<%=objRs("Figura")%>"></td>
</tr>
<tr>
<td width="199" bgcolor="#FFFFCC" height="36">
<p align="center"><input type="submit" name="Submit" value="Aggiungi"></td>
<td width="199" bgcolor="#FFFFCC" height="36"> </td>
</tr>
</table>
</form>
</center>

e questo del file che lo processa edit_process.asp


<%
cod=request.querystring("cod")
nome=Request.Form("nome")
indirizzo=Request.Form("indirizzo")
telefono=Request.Form("telefono")
fax=Request.Form("fax")
comune=Request.Form("comune")
provincia=Request.Form("provincia")
categoria=Request.Form("categoria")
figura=Request.Form("figura")
SQL="UPDATE tabella set nome='"&nome&"' ,indirizzo='"&indirizzo&"' ,telefono='"&telefono&"' ,fax='"&fax&"' ,comune='"&comune&"' ,provincia='"&provincia&"' ,categoria='"&categoria&"' ,figura='"&figura&"' WHERE id="&cod
objCn.Execute(SQL)
Response.Redirect "default.htm"
%>

Grazie per l'aiuto che vorrete darmi. Antonella