Grazie per la pazienza Trinità
ho visto il tuo codice....

list_cli = e.Item.FindControl("dd_client ")


cos'è dd_client

immagino sia l'id del textbox e proprio qui sta il mio problema:
come faccio a recuperare un id di un texBox generato automaticamente dalla funzione EditItemIndex = e.Item.ItemIndex


provo a postare tutto il codice:
<%@ Page Language="VB" Debug="true" %>
<%@ Import Namespace="System.Data" %>
<%@ Import Namespace="System.Data.OleDb" %>

<html>
<script runat="server">



Public Sub Page_Load(Sender As Object, E As EventArgs)
dim objConn as new OleDbConnection("Provider=IBMDA400; Data Source=192.168.0.51; User ID=WEBUSR; Password=WODSWEB")
Dim objCmd as new OleDbDataAdapter (("SELECT * FROM YFILEURO.DBSAN00F where F6 <> 'A'"), objConn)
'objConn.open 'Consiglio, Con l'oggetto OleDBDataAdapter non serve aprire la connessione.
Dim ds as DataSet = new DataSet()
objCmd.Fill(ds, "YFILEURO.DBSAM00F")
DataGrid1.DataSource=ds.Tables("YFILEURO.DBSAM00F" ).DefaultView

If not page.IsPostBack Then
DataBind()
End If
'objConn.close
End sub
'<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
sub DataGrid1_Edit(Obj As Object, e As DataGridCommandEventArgs)

DataGrid1.EditItemIndex = e.Item.ItemIndex
DataGrid1.DataBind()
end sub
'>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>

sub DataGrid1_Cancel(Obj As Object, e As DataGridCommandEventArgs)
DataGrid1.EditItemIndex = -1
DataGrid1.DataBind()
end sub
'>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>
sub DataGrid1_Update(Obj As Object, e As DataGridCommandEventArgs)

Dim IdAss as Integer = DataGrid1.DataKeys(e.Item.ItemIndex)
Dim Str1TxBx as TextBox =e.item.FindControl("?????? ")
dim Str1 as string = Str1TxBx.Text

Str1 = Str1.Replace("'", "'''")
'gli altri dati li recupero così e funziona
dim Str2 as string =(Ctype(e.Item.Cells(2).Controls(0), TextBox)).Text
dim Str3 as string =(Ctype(e.Item.Cells(3).Controls(0), TextBox)).Text
dim Str4 as string =(Ctype(e.Item.Cells(4).Controls(0), TextBox)).Text
dim Str5 as string =(Ctype(e.Item.Cells(5).Controls(0), TextBox)).Text

dim objConn1 as new OleDbConnection("Provider=IBMDA400; Data Source=192.168.0.51; User ID=WEBUSR; Password=WODSWEB; ")
Dim objCmd1 as new OleDbCommand(("UPDATE YFILEURO.DBSAM00F SET DESCRI='") & Str1 & ("', COSPDS = ") & Str2 & (", COSLIT = ") & Str3 & (", LISLIT = ") & Str4 & (", F6 = '") & Str5 & ("' where IDNPOS =")& Ctype(e.Item.Cells(0).Controls(1), Label).Text &(""), objConn1)
objConn1.Open
objCmd1.ExecuteNonQuery()

' toglie lo stato di edit
DataGrid1.EditItemIndex = -1
DataGrid1.DataBind()
objConn1.Close
dim objConn as new OleDbConnection("Provider=IBMDA400; Data Source=192.168.0.51; User ID=WEBUSR; Password=WODSWEB;")

Dim objCmd as new OleDbDataAdapter (("SELECT * FROM YFILEURO.DBSAN00F WHERE F6 <> 'A'"), objConn)
objConn.open

Dim ds as DataSet = new DataSet()
objCmd.Fill(ds, "YFILEURO.DBSAM00F")

DataGrid1.DataSource=ds.Tables("YFILEURO.DBSAN00F" ).DefaultView
DataGrid1.DataBind()
objConn.close
end sub
sub Page_IndexChanged (obj as Object, e as DataGridPageChangedEventArgs )
DataGrid1.CurrentPageIndex = e.NewPageIndex
Datagrid1.DataBind()
end Sub


</script>

<body>
<div align="center">
<table width="100%" border="0">
<tr>
<td>[img]../logo45mm.jpg[/img] </td>
<td><div align="right"><font color="#0000FF"><font size="4" face="Arial, Helvetica, sans-serif">Esempio
di modifica dati su db AS400</font></font> </div></td>
</tr>
</table>

</div>
<form runat="server">
<asp:datagrid id="DataGrid1" runat="server" BorderColor="#000000" GridLines="both" CellPadding="4" CellSpacing="0" Width="100%" Font-Name="Arial" Font-Size="7pt" ShowFooter="false" HeaderStyle-BackColor="#cccc99" FooterStyle-BackColor="#CCCC99" ItemStyle-BackColor="#FFFFFF" AlternatingItemStyle-BackColor="#CCCCCC" AutoGenerateColumns="false" OnEditCommand="DataGrid1_Edit" OnCancelCommand="DataGrid1_Cancel" OnUpdateCommand="Datagrid1_Update" AllowSorting="true" AllowPaging="true" PageSize="12" PagerStyle-NextPageText="Avanti" PagerStyle-PrevPageText="Indietro" PagerStyle-Font-Name="Courier" OnPageIndexChanged="Page_IndexChanged" PagerStyle-BackColor="#000000" PagerStyle-BorderWidth="1" PagerStyle-BorderColor="#000000" PagerStyle-ForeColor="#CCFFCC" PagerStyle-Mode="NumericPages">
<columns>
<asp:templatecolumn HeaderText="Pos" >
<itemtemplate>
<asp:label ID="Pos" runat="server" Text='<%# Container.DataItem("IDNPOS") %>' />
</itemtemplate>
</asp:templatecolumn >
<asp:templatecolumn HeaderText="Err" >
<itemtemplate>

</itemtemplate>
</asp:templatecolumn >
<asp:boundcolumn HeaderText="Località" DataField="DESCRI" />
<asp:boundcolumn HeaderText="Costo Sterline" DataField="COSPDS" />
<asp:boundcolumn HeaderText="COSTO Lire" DataField="COSLIT" />
<asp:boundcolumn HeaderText="Listino" DataField="LISLIT" />
<asp:boundcolumn HeaderText="Annulla" DataField="F6"/>
<asp:editcommandcolumn EditText="Edita" CancelText="Cancella" UpdateText="Aggiorna" ItemStyle-Wrap="false" HeaderText="Modifica/Cancella"/>
</columns>
</asp:datagrid>

</form>

</body></html> grazie et ciao