a data source instance has not been supplied for a data source error

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I'm currently trying to dynamically send an rdl report to my ReportViewer .net object.
I keep getting the error when I do it: A data source instance has not been supplied for the data source "blah"
I'm trying to define "blah" in my code behind at runtime.

ReportViewer1.ProcessingMode = Microsoft.Reporting.WebForms.ProcessingMode.Local;
  ReportViewer1.LocalReport.ReportPath = ReportFile;
  ReportViewer1.LocalReport.DataSources.Clear();
  Microsoft.Reporting.WebForms.ReportDataSource rds = new Microsoft.Reporting.WebForms.ReportDataSource();
  rds.Name = "blah";
  ReportViewer1.LocalReport.DataSources.Add(rds);
  ReportViewer1.DocumentMapCollapsed = true;
  ReportViewer1.LocalReport.Refresh();

this is not working by a long shot. I'm not sure what I'm supposed to do. here is an extract of the top of my rdl file:

  <DataSource Name="blah">
      <rd:DataSourceID>c6a8409e-71a4-4e96-86ad-b300a5b942c3</rd:DataSourceID>
      <ConnectionProperties>
        <DataProvider>SQL</DataProvider>
        <ConnectString>Data Source=10.555.121.121;Initial Catalog=blah</ConnectString>
        <IntegratedSecurity>true</IntegratedSecurity>
      </ConnectionProperties>
    </DataSource>
  </DataSources>

All I'm trying to do is simply select * from a table in "blah" in my report. I need this to work because I have many other report instances I need to show inside my ReportViewer. Why doesn't Microsoft make this easier?
Thanks in advance anybody...