This behavior has plagued me for at least a year now. If I refresh my workspace in Eclipse so that JasperStudio has to recompile the jasper files, several parameter classes that have always been on my classpath suddenly cannot be resolved by the JasperSoft Compiler. This happens with Luna and Mars. I am using the 6.1.1 version of the plugin in Eclipse Mars and Java 8 on Windows 8.1.
I have to go through all kinds of permutations like moving a graphical element on the report and saving for JasperStudio to finally find the classes. I want to stress that I have never had to make any changes to the parameter to get it to finally compile. Has anyone else ever encountered this behavior?