When I remove this line: "xssFCellStyle.getFont().getFamily();" from the program, the XLS file is generated OK, otherwise I get this error from excel 2010: "Excel found unreadable content in 'target.xlsx'. Do you want to recover..."
It's very hard with this little information about your problem. Can you provide some self-contained sample-code that allows to reproduce the problem? Preferably as patch/unit test so we can add it to the existing set of tests?
No info on actual problem, no test-file, no sample code => closing INVALID for now.