Apparently, when I add manually variable's initial value in the jrxml file (cf. code) or modify an existing (pre-3.5.2 created jrxml file) variable's initial value, everything is OK. However, when I create the variable in iReport and type in initial value, the error appears. So, for the moment, I have to create all my labels with iReport, position them, and then add initial values manually in jrxml file. Feasible, but cumbersome. Code: <initialValueExpression><![CDATA["test"]]></initialValueExpression>