long prevBarTime = history.getPreviousBarStart(Period.ONE_HOUR, history.getLastTick(Instrument.AUDCAD).getTime());
List<IBar> bars = history.getBars(Instrument.AUDCAD, Period.ONE_HOUR, OfferSide.BID, Filter.WEEKENDS,5000, prevBarTime,0);

on AUDCAD Hourly produces:

21:38:06 com.dukascopy.charts.data.datacache.DataCacheException: Cannot decode 7zip compressed file [...forex\cache\.cache\AUDCAD\2011\02\BID_candles_hour_1.bi5]

Less bars = no error.

All others are fine.

Seems that data on historical server has been reduced in order to get at least some stability. I'm getting following exception from JForex API

2012-01-18 06:14:03.673 WARN CurvesJsonProtocolHandler - Server returned HTTP response code: 403 for URL: https://www.dukascopy.com/datafeed/CHFJP ... hour_1.bi5
java.io.IOException: Server returned HTTP response code: 403 for URL: https://www.dukascopy.com/datafeed/CHFJP ... hour_1.bi5 at sun.net.www.protocol.http.HttpURLConnection.getInputStream(Unknown Source)

not only for CHFJPY but also for CADCHF, USDCHF, GBPCHF, AUDCHF and NZDCHF (converting to CHF as my base currency)

Same problem here. Each day when I start the platform there are gaps in the charts, that is the data is corrupt. On any instrument that I use. Time frames vary.
These problems have started just recently. I also use IHistory.getBars() to plot my own charts and it is a mess.