Check which version jasperreports.jar you are using..I got the same.I was using i-report 4.1.3 and jar file 3.7.0.Now i switch to jasperreports.4.1.3 and issue is resolved.
Joined: Jul 09, 2010
thank you for your answer, the problem is solved.
I spent iReport3.7.1 to iReport3.7.2, but when I copied the JAR iReport3.7.2 in the lib / directory of my project I have not removed the JAR iReport3.7.1.
I found the two JAR in this directory: that's the problem.