I use -ancf option few times in the command line. Apparently one of my filters has a problem, but all I get is this:
Exception in thread "main" java.lang.Error: Cannot create an instance of AncFilter: java.lang.NullPointerException
at com.sun.tdk.jcov.RepGen.generateReport(RepGen.java:235)
at com.sun.tdk.jcov.RepGen.generateReport(RepGen.java:183)
at com.sun.tdk.jcov.RepGen.generateReport(RepGen.java:168)
at com.sun.tdk.jcov.RepGen.run(RepGen.java:599)
at com.sun.tdk.jcov.tools.JCovCMDTool.run(JCovCMDTool.java:159)
at com.sun.tdk.jcov.RepGen.main(RepGen.java:320)

Judging by the message an NPE is caught somewhere and swallowed.