There has been a pretty serious bug in the community edition of JasperAnalysis apparently since the 5.6 release (a little over a month ago). The bug is described here: http://community.jaspersoft.com/jasperreports-server/issues/3694
It would seem that in order to debug this problem the jasperjpivot source is needed. According to the JasperReports-Server-CP-Source-Build-Guide.pdf, the jasperjpivot source can be obtained from the technical support website. Unfortunately a login is needed for this site which presumably is only available to those with support contracts.
Is the jasperjpivot source available from somewhere else?
JPivot is another open source project. Jaspersoft is using jar from several other open source projects. You'll need to get sources for these projects from respective project pages.