Testing a new version of JETT 0.11.0, I found this problem: Exception in thread "Thread-500" java.lang.NoSuchMethodError: org.apache.poi.ss.usermodel.Font.getBoldweight()S at net.sf.jett.model.CellStyleCache.getRepresentation(CellStyleCache.java:223) at net.sf.jett.model.CellStyleCache.getRepresentation(CellStyleCache.java:174) at net.sf.jett.model.CellStyleCache.cacheCellStyle(CellStyleCache.java:143) at net.sf.jett.model.CellStyleCache.cachePreExistingCellStyles(CellStyleCache.java:62) at net.sf.jett.model.CellStyleCache.<init>(CellStyleCache.java:50)...