Bug in iReport while sorting?

[nikunj321]

I have xml as a datasource,

1.I am having one grouping in my report and my grouping field has values like 1,01,2,2,02,1,01,....

So I am grouping by this field and in sort option i m setting this field to get sorted on the field and it gives proper output.

2.In my report header i have to include one subreport since i want to print one iterated value in Report header band(adding virtual detail band by adding a subreport with detail band only in report header band)

Due to my report requirement I have to use a sort option and subreport,but when i run the main report ,it shows the error

"Error filling print :Error Evalauting expression

Source text:((net.sf.jasperreports.engine.data.JRXmlDataSource)
    $P{REPORT_DATA_SOURCE}).dataSource("/node/dummyxpath")"

When i run the same report by removing a fied in sort option it gives output...but when i have sorting and subreport it gives above error..

Please guide me...