Error when trying to retain updatepanel values - asp.net

Question

I'm having a problem with a couple of dropdown boxes in my gridview losing their values upon postback.
Everything is within an update panel so I have tried to include into my code but this just throws an exception. See the below code, I have a child gridview within a larger one:
I am receiving the following exception when I go to load the gridview: A control with ID 'DropDownNote' could not be found for the trigger in UpdatePanel 'UpdateGV'.
I followed what was in this post: Control in UpdatePanel loses value
But now I'm getting the above exception, what am I missing here? Will solving this problem retain the values of the dropdowns after the postback?
<asp:ScriptManager ID="ScriptManager1" runat="server" EnablePartialRendering="true">
</asp:ScriptManager>
<asp:GridView ID="GVAccounts" runat="server" AutoGenerateColumns="False"
CellPadding="4" ForeColor="#333333"
GridLines="Horizontal"
style="position: relative; margin-top: 10px">
<AlternatingRowStyle BackColor="White" ForeColor="#284775" />
<Columns>
<asp:BoundField DataField="branch" HeaderText="Branch"
SortExpression="branch" />
<asp:BoundField DataField="no" HeaderText="Account"
SortExpression="account" />
<asp:TemplateField HeaderText="Name" SortExpression="name">
<EditItemTemplate>
<asp:TextBox ID="TextName" runat="server" Text='<%# Eval("name") %>'></asp:TextBox>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="LabelName" runat="server" Text='<%# Eval("name") + " " + Eval("surname") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:BoundField DataField="type" HeaderText="Type" SortExpression="type" />
<asp:BoundField DataField="sub" HeaderText="Sub" SortExpression="sub" />
<asp:BoundField DataField="TotalAmount" HeaderText="Hold"
SortExpression="TotalAmount" />
<asp:BoundField DataField="loc" HeaderText="LOC" DataFormatString="{0:C}" SortExpression="loc" />
<asp:BoundField DataField="locstatus" HeaderText="LOC status"
SortExpression="locstatus" />
<asp:BoundField DataField="HoldCalc" HeaderText="OD/EX Amt" SortExpression="HoldCalc" />
<asp:BoundField DataField="odtimes" HeaderText="#OD" SortExpression="odtimes" />
<asp:TemplateField>
<ItemTemplate>
<tr>
<td colspan="100%">
<div id="gridChild" style="display: inline; position: relative; left: 15px; overflow: auto">
<asp:UpdatePanel ID="UpdateGV" runat="server" UpdateMode="Conditional">
<ContentTemplate>
<asp:GridView ID="gvChildGrid" runat="server" AutoGenerateColumns="false"
BorderStyle="Double" BorderColor="#5D7B9D" Width="80%">
<HeaderStyle BackColor="#5D7B9D" Font-Bold="true" ForeColor="White" />
<RowStyle BackColor="#E1E1E1" />
<AlternatingRowStyle BackColor="White" />
<HeaderStyle BackColor="#5D7B9D" Font-Bold="true" ForeColor="White" />
<Columns>
<asp:TemplateField HeaderText="Select">
<ItemTemplate>
<asp:CheckBox ID="chkSelect" runat="server" AutoPostBack="true"
oncheckedchanged="chkSelect_CheckedChanged" />
</ItemTemplate>
</asp:TemplateField>
<asp:BoundField DataField="effective" HeaderText="Effective" HeaderStyle-HorizontalAlign="Left" />
<asp:BoundField DataField="desc_" HeaderText="Desc" HeaderStyle-HorizontalAlign="Left" />
<asp:BoundField DataField="code" HeaderText="TC" HeaderStyle-HorizontalAlign="Left" />
<asp:BoundField DataField="amount" HeaderText="Amount" HeaderStyle-HorizontalAlign="Left" />
<asp:BoundField DataField="tracer" HeaderText="Cheq #" HeaderStyle-HorizontalAlign="Left" />
<asp:BoundField DataField="empltype" HeaderText="Empl" HeaderStyle-HorizontalAlign="Left" />
<asp:BoundField DataField="balance" HeaderText="OD/EXT Amt" HeaderStyle-HorizontalAlign="Left" />
<asp:TemplateField HeaderText="Note">
<ItemTemplate>
<asp:DropDownList ID="DropDownNote" runat="server"
onselectedindexchanged="DropDownNote_SelectedIndexChanged"
AutoPostBack="True">
<asp:ListItem></asp:ListItem>
<asp:ListItem>MWC</asp:ListItem>
<asp:ListItem>CBM</asp:ListItem>
<asp:ListItem>Return</asp:ListItem>
<asp:ListItem>TSF</asp:ListItem>
<asp:ListItem>OK NO S/C</asp:ListItem>
</asp:DropDownList>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Note1">
<ItemTemplate>
<asp:DropDownList ID="ddNote2" runat="server">
<asp:ListItem Selected="True">NSF</asp:ListItem>
<asp:ListItem>Funds Not Clear</asp:ListItem>
<asp:ListItem>Post Dated</asp:ListItem>
<asp:ListItem>Stale Dated</asp:ListItem>
<asp:ListItem>Stop Payment</asp:ListItem>
<asp:ListItem>Encoding Incorrect</asp:ListItem>
</asp:DropDownList>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Branch">
<ItemTemplate>
<asp:DropDownList ID="ddBranch" runat="server" DataSourceID="BranchDataSource"
DataTextField="branch" DataValueField="branch">
</asp:DropDownList>
<asp:SqlDataSource ID="BranchDataSource" runat="server"
ConnectionString="<%$ ConnectionStrings:ThirdPartyDataConnectionString %>"
SelectCommand="SELECT [branch] FROM [branch]"></asp:SqlDataSource>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Account">
<ItemTemplate>
<asp:TextBox ID="TextNo" runat="server" ></asp:TextBox>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Type">
<ItemTemplate>
<asp:DropDownList ID="ddType" runat="server" DataSourceID="typeSource"
DataTextField="Type" DataValueField="Type">
</asp:DropDownList>
<asp:SqlDataSource ID="typeSource" runat="server"
ConnectionString="<%$ ConnectionStrings:ThirdPartyDataConnectionString %>"
SelectCommand="SELECT [Type] FROM [DMDType]"></asp:SqlDataSource>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Sub">
<ItemTemplate><asp:TextBox ID="TextSub" Width="25px" runat="server"></asp:TextBox></ItemTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>
</ContentTemplate>
<Triggers>
<asp:AsyncPostBackTrigger ControlID="DropDownNote" EventName="SelectedIndexChanged" />
</Triggers>
</asp:UpdatePanel>
</div>
</td>
</tr>
</ItemTemplate>
</asp:TemplateField>
</Columns>
<EditRowStyle BackColor="#999999" />
<FooterStyle BackColor="#5D7B9D" Font-Bold="True" ForeColor="White" />
<HeaderStyle BackColor="#5D7B9D" Font-Bold="True" ForeColor="White" />
<PagerStyle BackColor="#284775" ForeColor="White" HorizontalAlign="Center" />
<RowStyle BackColor="#F7F6F3" ForeColor="#333333" />
<SelectedRowStyle BackColor="#E2DED6" Font-Bold="True" ForeColor="#333333" />
<SortedAscendingCellStyle BackColor="#E9E7E2" />
<SortedAscendingHeaderStyle BackColor="#506C8C" />
<SortedDescendingCellStyle BackColor="#FFFDF8" />
<SortedDescendingHeaderStyle BackColor="#6F8DAE" />
</asp:GridView>

Answer 1

I decided to go a different route with this, I added MaintainScrollPositionOnPostback="true" to the top line of the aspx, since the complaint from the client was that the page would go back to the top after every postback. I had originally used the UpdatePanel to remedy this but decided this would be a better option.
Now my only problem is getting the page to retain the values of the dropdown boxes after a postback which I will have to figure out how that can be done.