following is the stack trace.

java.lang.IllegalArgumentException: the region is illegal A47:H48[47,0,46,7]
at org.zkoss.zss.model.CellRegion.checkLegal(CellRegion.java:79)
at org.zkoss.zss.model.CellRegion.<init>(CellRegion.java:91)
at org.zkoss.zss.model.impl.pdf.PdfExporter.splitRegionsInBoundaries(PdfExporter.java:1264)
at org.zkoss.zss.model.impl.pdf.PdfExporter.layoutCharts(PdfExporter.java:1644)
at org.zkoss.zss.model.impl.pdf.PdfExporter.access$26(PdfExporter.java:1606)
at org.zkoss.zss.model.impl.pdf.PdfExporter$PdfHeaderFooter.doEndPage(PdfExporter.java:2644)
at org.zkoss.zss.model.impl.pdf.PdfExporter$PdfHeaderFooter.onEndPage(PdfExporter.java:2606)
at com.lowagie.text.pdf.PdfDocument.newPage(Unknown Source)
at com.lowagie.text.pdf.PdfDocument.close(Unknown Source)
at com.lowagie.text.Document.close(Unknown Source)
at org.zkoss.zss.model.impl.pdf.PdfExporter.export(PdfExporter.java:258)
at org.zkoss.zss.api.impl.ExporterImpl.export(ExporterImpl.java:49)
at org.zkoss.zss.app.repository.impl.BookUtil.saveBookToWorkingFolder(BookUtil.java:133)
at org.zkoss.zss.app.ui.AppCtrl.doExportPdf(AppCtrl.java:349)
at org.zkoss.zss.app.ui.AppCtrl.onAppEvent(AppCtrl.java:375)
at org.zkoss.zss.app.ui.CtrlBase$1.onEvent(CtrlBase.java:64)
at org.zkoss.zk.ui.AbstractComponent.onEvent(AbstractComponent.java:2752)
at org.zkoss.zk.ui.AbstractComponent.service(AbstractComponent.java:2723)
at org.zkoss.zk.ui.AbstractComponent.service(AbstractComponent.java:2664)
at org.zkoss.zk.ui.impl.EventProcessor.process(EventProcessor.java:136)
at org.zkoss.zk.ui.impl.UiEngineImpl.processEvent(UiEngineImpl.java:1765)
at org.zkoss.zk.ui.impl.UiEngineImpl.process(UiEngineImpl.java:1550)
at org.zkoss.zk.ui.impl.UiEngineImpl.execUpdate(UiEngineImpl.java:1260)
at org.zkoss.zk.au.http.DHtmlUpdateServlet.process(DHtmlUpdateServlet.java:603)
at org.zkoss.zk.au.http.DHtmlUpdateServlet.doGet(DHtmlUpdateServlet.java:485)
at org.zkoss.zk.au.http.DHtmlUpdateServlet.doPost(DHtmlUpdateServlet.java:494)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:820)
at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511)
at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:401)
at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:766)
at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:450)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at org.mortbay.jetty.Server.handle(Server.java:326)
at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:945)
at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:756)
at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:218)
at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:410)
at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:582)