The new Findbugs version produces a findbugs-result.xml with invalid character entity, or the FindbugsXmlReportParser can't handle the entity.
My class that can't be analysed contains a String s1 = '\uffff' + "_YELLOW_FLAG" (used for sorting, to be placed last). The String s2 = '\u0000' + "_GREEN_FLAG" seems to be handled correctly.
The string s1 produces the xml element: <String value="_YELLOW_FLAG" role="STRING_CONSTANT"> which causes the problem.
This error occurred after upgrading from Sonar3.0 to Sonar3.2, I guess it comes from the use of Findbugs 2?