Update is not picking up current value of text box

[Webskater]

Here is an extract of some code on a webform. The code is within a GridView called gvContactSummary.

<asp:TemplateField HeaderText="Details">
    <ItemTemplate>
        <asp:HyperLink ID="hlDetails" runat="server"></asp:HyperLink>
        <asp:Label runat="server" ID="lblDescription" Text="" ToolTip='<%# Eval("Description")%>' />
    </ItemTemplate>
    <EditItemTemplate>
        <asp:TextBox runat="server" ID="txtValue" Text='<%# Eval("Details")%>' CssClass="NormalTextbox"
            Width="320px" />
    </EditItemTemplate>
</asp:TemplateField>

when you click the edit link that appears a bit further across the grid the 'EditItemTemplate' is displayed and the Textbox with ID="txtValue" appears - with the correct data to edit displayed in it.

If I change the data in the text box and click Update this happens ... (just an extract)

            DataAccess da = new DataAccess();
            GridViewRow row = gvContactSummary.Rows[e.RowIndex];
            Label AIID = (Label)row.FindControl("AIID");
            Label LocationID = (Label)row.FindControl("LocationID");
            Label Type = (Label)row.FindControl("lblType");
            TextBox txtVal = (TextBox)row.FindControl("txtValue");

            if (AIID.Text != "0")
            {
                //Update Addn info ID
                string Description = "";
                da.UpdateContactAddnContactInfo(Convert.ToInt32(AIID.Text), txtVal.Text, Description);
            }

Now I know the update is happening correctly because if I hard code the value of the text box 'txtValue' this hard-coded value is then written to the database when Update is clicked.

But, when it is not hardcoded - ie. when the textbox contains a value from the database (in this case a phone number) then ...

If I click Edit- the textbox appears and I remove the existing phone number, enter a new one and click Update. But the value of txtVal.Text is showing the number before I edited it.

Can anyone explain why, when the Update link is clicked, txtVal.Text does not contain the current value of the text box txtValue - it contains the original value.

Thanks for any help. Spent all afternoon on this and got nowhere!