Hi,
I'm using just the following lines of code:
rptView.LocalReport.DataSources.Clear();
rptView.LocalReport.DataSources.Add(ds);
rptView.LocalReport.Refresh();
and this is from the page design
<rsweb:ReportViewer ID="rptView" runat="server" Width="9.25in" Visible="False">
<localreport reportpath="Reports\User_Monthly_Report.rdlc">
</localreport>
</rsweb:ReportViewer>
Maybe you should set the path to local report also, and also check if the datasource name is corect (like the one in report definition).