Update panel not working with gridview - ASP.NET/VB.NET

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VB

ASP.NET

Gridview

UpdatePanel

When I click the image button 'imgPaymentMethod' I require the code to change the ImageUrl of the Image Button. However, nothing happens when clicked.

<asp:GridView ID="gdvItems" runat="server" AutoGenerateColumns="False"
     DataKeyNames="fileID" DataSourceID="DSUploadedItems" CssClass="mGrid"
     AlternatingRowStyle-CssClass="alt">
 <AlternatingRowStyle CssClass="alt"></AlternatingRowStyle>
     <Columns>
         <asp:TemplateField visible="true" HeaderText="Price">
             <ItemTemplate>
                 <asp:DropDownList ID="ddlBuyPrice" runat="server" AutoPostBack="True" Font-Size="11px" Height="22px" OnSelectedIndexChanged="ddlBuyPrice_SelectedIndexChanged" SelectedValue='<%# Bind("buyPrice")%>'>
                      <asp:ListItem Value="0.00">Select:</asp:ListItem>
                 </asp:DropDownList>
                 <asp:LinkButton visible="false" ID="lnkPaymentMethod" runat="server" CausesValidation="False"
                     Text='<%# Bind("acceptPaypal")%>' > /></asp:LinkButton>
                 <br /><br />
                 <asp:Label ID="lblSoldStatus" visible="false" runat="server" CausesValidation="False" Text='<%# Bind("sold") %>' />
                 <asp:Image ID="imgSoldStatus" alt="Sold Status" runat="server" width="100px" ImageUrl="~/files/images/icons/iconSold.png" />
                 <br />

                 <asp:UpdatePanel ID="upPnlControls" style="margin-top:0px;" runat="server" UpdateMode="Conditional" ChildrenAsTriggers="false">
                     <Triggers>
                         <asp:AsyncPostBackTrigger controlid="imgPaymentMethod" eventname="Click" />
                     </Triggers>
                     <ContentTemplate>
                         <asp:ImageButton visible="true" ID="imgPaymentMethod" runat="server" CausesValidation="False" width="50px" onclick="lnkPaymentMethod_Click"></asp:ImageButton>
                     </ContentTemplate>
                 </asp:UpdatePanel>

                 <br />
                 <asp:Label ID="lblDateBought" runat="server" CausesValidation="False" Text='<%# Bind("dateBought") %>' />
                 <asp:LinkButton ID="lnkMarkAsSold" runat="server"  OnClick="markAsSold_Click" Text="Mark As Sold" Visible="true" ></asp:LinkButton>
             </ItemTemplate>
         </asp:TemplateField>
     </Columns>
 </asp:GridView>

VB Code..

Protected Sub lnkpaymentMethod_Click(sender As Object, e As System.EventArgs)
    Dim imgPaymentMethod As ImageButton = CType(sender, ImageButton)
    Dim currentRow As GridViewRow = DirectCast(imgPaymentMethod.Parent.Parent, GridViewRow)

    If imgPaymentMethod.ImageUrl="~/files/images/icons/paypalIcon.gif" Then
        imgPaymentMethod.ImageUrl="~/files/images/icons/cashIcon.gif"
    Else
        imgPaymentMethod.ImageUrl="~/files/images/icons/paypalIcon.gif"
    End If

End Sub

What I have tried:

I have tried moving the Gridview inside the Update Panel but then I get this error:

Quote:

A control with ID 'imgPaymentMethod' could not be found for the trigger in UpdatePanel 'upPnlControls'