'The ConnectionString property has not been initialized' won't go away - asp.net

Question

I've been getting this error for over a day now and can't afford to waste time when my deadline is tight. Similar code works and I can't see the difference and why this code is giving this error. When I try to update the changes I edit on my gridview the error occurs.
my markup:
<asp:GridView ID="diary" runat="server" AutoGenerateColumns="False" DataSourceID="sDiary"
DataKeyNames="DiaryId" EnableViewState="False">
<Columns>
<asp:BoundField DataField="DiaryId" HeaderText="DiaryId" InsertVisible="False" ReadOnly="True"
SortExpression="DiaryId" Visible="False" />
<asp:BoundField DataField="DiaryItem" HeaderText="DiaryItem" SortExpression="DiaryItem">
<HeaderStyle HorizontalAlign="Left" />
</asp:BoundField>
<asp:BoundField DataField="DiaryDate" HeaderText="DiaryDate" SortExpression="DiaryDate">
<HeaderStyle HorizontalAlign="Left" />
</asp:BoundField>
<asp:CommandField ShowEditButton="True" />
</Columns>
</asp:GridView>
<asp:SqlDataSource ID="sDiary" runat="server" SelectCommand="SELECT DiaryItem, left(convert(varchar,DiaryDate,120),10) as DiaryDate, DiaryId FROM a_Diary WHERE CustomerId=#CustomerId And ProcessedDate is null ORDER BY DiaryDate"
UpdateCommand="UPDATE a_Diary SET DiaryItem=#DiaryItem, DiaryDate=#DiaryDate WHERE DiaryId=#DiaryId">
<SelectParameters>
<asp:Parameter Name="CustomerId" />
</SelectParameters>
<UpdateParameters>
<asp:Parameter Name="DiaryId" Type="Int32" />
<asp:Parameter Name="DiaryItem" Type="String" />
<asp:Parameter Name="DiaryDate" Type="DateTime" />
</UpdateParameters>
</asp:SqlDataSource>
code behind:
protected void Page_Load(object sender, EventArgs e)
{
sDiary.ConnectionString = ConfigurationManager.ConnectionStrings["BZSSSqlConnectionString"].ConnectionString;
sDiary.SelectParameters["CustomerId"].DefaultValue = Request.QueryString["c"];
}
Can anyone help me?