Regarding excel sheet datasource of subreport

Hi,

I am new to iReports and currently i am using iReport 4.0.2.Please someone help me in my query

I have a main report which has a subreport in it.The subreport retreives data from excel sheet.I followed following steps to retreive data

1..In subreport properties i chose connection type as datasource expression.

2.In datasource expressioni wrote new net.sf.jasperreports.engine.data.JRXlsDataSource(new File("path of xls file"))

When i compile subreport individually it gives report correctly but when i try to retreive data through main report it gives me following error

Error filling print...net.sf.jasperreports.engine.JRException:Unknown Column name:XYZ

Thanks and Regards