com-jaspersoft-ireport.jar is missing JRXmlWriter_n_n_n.class classes, where "n_n_n" is earlier that "3_5_0".
In my case, I need to be able to save to 2_0_5 and 3_0_0, due to constraints of installed purchased software.
Options/iReport/General/Compatibility has a drop down box which lists versions of iReport all the way back to JasperReports 2.0.2.
I called the severity "minor" only because I have the option of installing and using iReport versions 2.0.5 (to which version I must compile subreports) and 3.0 (which works with our purchased software for uncompiled primary report JRXMLs).
I have a newly installed installation of iReport 4.5.0.