Still can't see why I'm getting this error!

[Tim::..]

I keep getting the following error on a dropdownlist control I have added to a datagrid! I have given the control the correct id and don't get any errors when conpiling the code but as soon as I try to access the page I receive the error show below!

Can someone please tell me why and how I might fix it!

Thanks!

ERROR: Object reference not set to an instance of an object.
...::INLINE CODE
<asp:datagrid id="DGPages" runat="server" OnDeleteCommand="DGPages_Delete" OnCancelCommand="DGPages_Cancel"
OnUpdateCommand="DGPages_Update" OnEditCommand="DGPages_Edit" DataKeyField="pageID" AutoGenerateColumns="False" Width="90%" CellPadding="4" EditItemStyle-BackColor="#eeeeee" HeaderStyle-BackColor="Black" HeaderStyle-ForeColor="White" HeaderStyle-HorizontalAlign="Center" HeaderStyle-Font-Bold="True" ShowFooter="True">
<Columns>
<asp:TemplateColumn HeaderText="ID">
<ItemTemplate>
<%# Container.DataItem("pageID") %>
</ItemTemplate>
<EditItemTemplate>
<%# Container.DataItem("pageID") %>
</EditItemTemplate>
</asp:TemplateColumn>
<asp:TemplateColumn HeaderText="Description">
<ItemTemplate>
<%# Container.DataItem("description") %>
</ItemTemplate>
<EditItemTemplate>
<asp:TextBox ID="description" Columns="5" Text='<%# Container.DataItem("description") %>' Runat="server" />
</EditItemTemplate>
<FooterTemplate>
<asp:TextBox ID="add_Description" Columns="5" Runat="Server" />
</FooterTemplate>
</asp:TemplateColumn>
<asp:TemplateColumn HeaderText="Title">
<ItemTemplate>
<%# Container.DataItem("header") %>
</ItemTemplate>
<EditItemTemplate>
<asp:TextBox ID="title" Columns="5" Text='<%# Container.DataItem("header") %>' Runat="server" />
</EditItemTemplate>
<FooterTemplate>
<asp:TextBox ID="add_title" Columns="5" Runat="Server" />
</FooterTemplate>
</asp:TemplateColumn>
<asp:TemplateColumn HeaderText="Office">
<ItemTemplate>
</ItemTemplate>
<EditItemTemplate>
<asp:TextBox ID="office" Columns="5" Text='<%# Container.DataItem("offName") %>' Runat="server" />
</EditItemTemplate>
<FooterTemplate>
<!-- Pull Office Names from Database -->
<asp:DropDownList id="add_Office" runat="server"></asp:DropDownList>
</FooterTemplate>
</asp:TemplateColumn>
<asp:EditCommandColumn ButtonType="PushButton" UpdateText="Update" CancelText="Cancel" EditText="Edit" HeaderText="Edit"></asp:EditCommandColumn>
<asp:TemplateColumn HeaderText="Delete">
<FooterTemplate>
<asp:Button CommandName="Insert" Text="Add" ID="btnAdd" Runat="server" />
</FooterTemplate>
<ItemTemplate>
<asp:Button CommandName="Delete" Text="Delete" ID="btnDel" Runat="server" />
</ItemTemplate>
</asp:TemplateColumn>
</Columns>
</asp:datagrid>

...:: CODE BEHIND
Sub PopulateDropdown()
' Only pull data from db on first page call.
If Not Page.IsPostBack Then
' Create connection
Dim Myconn As New SqlConnection(ConfigurationSettings.AppSettings("s trConn"))
Dim cmd As New SqlCommand("SelectOffice", Myconn)
cmd.CommandType = CommandType.StoredProcedure

Myconn.Open()

' Get a new datareader from our command
Dim myReader As SqlDataReader = cmd.ExecuteReader()
add_Office.DataSource = myReader ' *** ERROR HERE
add_Office.DataValueField = "officeID"
add_Office.DataTextField = "offName"
add_Office.DataBind()

myReader.Close()

Myconn.Close()
End If
End Sub