How to change (Crystal Report )subreport's datasource or report file in runtime ?

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ADO.NET

C#3.5

CrystalReports

I have question regarding crystal reports.
Please tell me how can i change subreport's report file in runtime.

if i tried following then it gave me eroor "Not supported within subreports."
MainReport rpt=new MainReport();
rpt.SubReports[0].Load("Report1.rpt");