problems with jasperreport

[Ed]

I have to do some reports in jasper report.
I need the function that generates the pdf files
When I execute the applet in the server, this error appears:

net.sf.jasperreports.engine.JRException: Error loading expression
class : reporte_multiple_1179164041828_887410
at
net.sf.jasperreports.engine.design.JRAbstractJavaCompiler.loadEvaluator(JRAbstractJavaCompiler.java:87)
at
net.sf.jasperreports.engine.design.JRAbstractCompiler.loadEvaluator(JRAbstractCompiler.java:320)
at
net.sf.jasperreports.engine.design.JRDefaultCompiler.loadEvaluator(JRDefaultCompiler.java:218)
at
net.sf.jasperreports.engine.fill.JRFillDataset.createCalculator(JRFillDataset.java:410)
at
net.sf.jasperreports.engine.fill.JRBaseFiller.<init>(JRBaseFiller.java:384)
at
net.sf.jasperreports.engine.fill.JRVerticalFiller.<init>(JRVerticalFiller.java:77)
at
net.sf.jasperreports.engine.fill.JRVerticalFiller.<init>(JRVerticalFiller.java:59)
at
net.sf.jasperreports.engine.fill.JRFiller.createFiller(JRFiller.java:147)
....

what is happening?

[Heather]

don't waste your time
I recommend this tool
iText: Generate PDF files with Java

[Peter]

May be your application don't have permission to load class. You should insert these line into
%install_dir%/appserver/domains/your_domain/config/server.policy file

--------------begin----------------
grant {
permission java.lang.RuntimePermission "createClassLoader";
};
---------------end---------------------