Ireport 3.7.1 Invalid byte 1 of 1-byte UTF-8

[kami022004]

Hello
I created an application using jasperreport that converts an xml data source to pdf.

I used iReport 3.7.1 to generate a .jasper file that I used in my application to dynamically load data from the xml source into my report.
I run my program 2 times and it worked fine-> the pdf report was generated.
But just after I got this error:

net.sf.jasperreports.engine.JRException: org.apache.xerces.impl.io.MalformedByteSequenceException: Invalid byte 1 of 1-byte UTF-8 sequence.

I tied ALL the solution found on the net (resaving the jrxml as utf-8 , installing the java and xml plugin, editing the ireport.conf file) and without any issue.
This is the 5 th day of debugging, and I am tired plz help :(