Problem in creating sub report - Accessing the result set failed

Question

I am using JfreeReport. I don't succeed to run a report with sub reoport inside. The report was designed by Report Designer 3.0. The error is:
org.jfree.report.modules.misc.tablemodel.DataTableException: Accessing the result set failed:
.....
ParentException:
org.postgresql.util.PSQLException: This ResultSet is closed.

The code is:

DriverConnectionProvider provider = new DriverConnectionProvider();  
provider.setDriver(Configuration.getPostgreSQLDriver());  
provider.setProperty("user", Configuration.getPostgreSQLConnectionUsername());  
provider.setProperty("password", Configuration.getPostgreSQLConnectionPassword());  
provider.setUrl(Configuration.getPostgreSQLConnectionUrl() + 
                Configuration.getRsDbName());  
SQLReportDataFactory dataFactory = new SQLReportDataFactory(provider);  

dataFactory.setQuery("default", _query);  
dataFactory.setQuery("sub1",
                "SELECT url AS \"URL\"," +
                "tran_time AS \"TRAN_TIME\"" +
                " FROM trans WHERE" +
                " url = ${TRANS_URL}");  
report.setDataFactory(dataFactory); 

If I limit the default query to return one row only, I get the report as desired with the sub report.

What is wrong? Why I can't get a reports with data and sub data for wach row?

Thanks in advance!