Problemas com crosstab no ireport

bom dia galerinha do GUJ… estou precisando de ajuda preciso criar um relatório ordenado por mês com os valores gastos por cada cliente durante o ano, tentei com o componente table do ireport mais consegui, agora estou tentando usar crosstab mais esta dando o seguinte erro…
Error filling print… Could not create bucketing service
net.sf.jasperreports.engine.JRRuntimeException: Could not create bucketing service at net.sf.jasperreports.engine.fill.JRFillCrosstab.initBucketingService(JRFillCrosstab.java:540) at net.sf.jasperreports.engine.fill.JRFillCrosstab$JRFillCrosstabDataset.customInitialize(JRFillCrosstab.java:777) at net.sf.jasperreports.engine.fill.JRFillElementDataset.initialize(JRFillElementDataset.java:134) at net.sf.jasperreports.engine.fill.JRCalculator.initializeDataset(JRCalculator.java:529) at net.sf.jasperreports.engine.fill.JRCalculator.initializeVariables(JRCalculator.java:295) at net.sf.jasperreports.engine.fill.JRFillDatasetRun.init(JRFillDatasetRun.java:229) at net.sf.jasperreports.engine.fill.JRFillDatasetRun.iterate(JRFillDatasetRun.java:187) at net.sf.jasperreports.engine.fill.JRFillDatasetRun.evaluate(JRFillDatasetRun.java:156) at net.sf.jasperreports.engine.fill.JRFillElementDataset.evaluateDatasetRun(JRFillElementDataset.java:224) at net.sf.jasperreports.engine.fill.JRFillCrosstab.evaluate(JRFillCrosstab.java:472) at net.sf.jasperreports.engine.fill.JRFillElementContainer.evaluate(JRFillElementContainer.java:257) at net.sf.jasperreports.engine.fill.JRFillBand.evaluate(JRFillBand.java:457) at net.sf.jasperreports.engine.fill.JRVerticalFiller.fillSummaryNoLastFooterSamePage(JRVerticalFiller.java:1083) at net.sf.jasperreports.engine.fill.JRVerticalFiller.fillSummary(JRVerticalFiller.java:1048) at net.sf.jasperreports.engine.fill.JRVerticalFiller.fillReportEnd(JRVerticalFiller.java:312) at net.sf.jasperreports.engine.fill.JRVerticalFiller.fillReport(JRVerticalFiller.java:151) at net.sf.jasperreports.engine.fill.JRBaseFiller.fill(JRBaseFiller.java:909) at net.sf.jasperreports.engine.fill.JRBaseFiller.fill(JRBaseFiller.java:841) at net.sf.jasperreports.engine.fill.JRFiller.fill(JRFiller.java:88) at net.sf.jasperreports.engine.JasperFillManager.fill(JasperFillManager.java:653) at net.sf.jasperreports.engine.JasperFillManager.fill(JasperFillManager.java:569) at net.sf.jasperreports.engine.JasperFillManager.fillReport(JasperFillManager.java:915) at com.jaspersoft.ireport.designer.compiler.IReportCompiler.run(IReportCompiler.java:928) at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:572) at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:997) Caused by: net.sf.jasperreports.engine.JRException: The bucket expression values are not comparable and no comparator specified. at net.sf.jasperreports.crosstabs.fill.calculation.BucketDefinition.(BucketDefinition.java:100) at net.sf.jasperreports.engine.fill.JRFillCrosstab.createServiceBucket(JRFillCrosstab.java:425) at net.sf.jasperreports.engine.fill.JRFillCrosstab.createService(JRFillCrosstab.java:382) at net.sf.jasperreports.engine.fill.JRFillCrosstab.initBucketingService(JRFillCrosstab.java:536) … 24 more
Print not filled. Try to use an EmptyDataSource…

estou usando jrbeancollectiondatasource para passar os dados…
alguem pode me ajudar…

ninguém estou precisando mto de ajuda

ja resolvi meu problema vlw