type 12 is not a valid type

Hi all,
I'm using exist embedded with cocoon. In a random way I'm
getting quite frequently the exception presented bellow.
Does anyone has any idea what's going on here?

Thanks for any help.

-> Cocoon -> 2.1.5
-> eXist -> eXist-1.0b1
-> JDK -> 1.4.2_04

Original Exception: org.apache.cocoon.ProcessingException: Failed to execute
pipeline.: java.lang.IllegalArgumentException: type 12 is not a valid type
        at
org.apache.cocoon.components.pipeline.AbstractProcessingPipeline.processXMLPipeline(AbstractProcessingPipeline.java:552)
        at
org.apache.cocoon.components.pipeline.impl.AbstractCachingProcessingPipeline.processXMLPipeline(AbstractCachingProcessingPipeline.java:173)
        at
org.apache.cocoon.components.pipeline.AbstractProcessingPipeline.process(AbstractProcessingPipeline.java:681)
        at
org.apache.cocoon.components.source.impl.SitemapSource.toSAX(SitemapSource.java:432)
        at 
org.apache.cocoon.components.source.SourceUtil.parse(SourceUtil.java:247)
        at
org.apache.cocoon.sitemap.ContentAggregator.generate(ContentAggregator.java:125)
        at
org.apache.cocoon.components.pipeline.AbstractProcessingPipeline.processXMLPipeline(AbstractProcessingPipeline.java:545)
        at
org.apache.cocoon.components.pipeline.impl.AbstractCachingProcessingPipeline.processXMLPipeline(AbstractCachingProcessingPipeline.java:173)
        at
org.apache.cocoon.components.pipeline.AbstractProcessingPipeline.process(AbstractProcessingPipeline.java:490)
        at
org.apache.cocoon.components.treeprocessor.sitemap.SerializeNode.invoke(SerializeNode.java:120)
        at
org.apache.cocoon.components.treeprocessor.AbstractParentProcessingNode.invokeNodes(AbstractParentProcessingNode.java:49)
        at
org.apache.cocoon.components.treeprocessor.sitemap.ActTypeNode.invoke(ActTypeNode.java:138)
        at
org.apache.cocoon.components.treeprocessor.AbstractParentProcessingNode.invokeNodes(AbstractParentProcessingNode.java:49)
        at
org.apache.cocoon.components.treeprocessor.sitemap.ActTypeNode.invoke(ActTypeNode.java:138)
        at
org.apache.cocoon.components.treeprocessor.AbstractParentProcessingNode.invokeNodes(AbstractParentProcessingNode.java:49)
        at
org.apache.cocoon.components.treeprocessor.sitemap.ActTypeNode.invoke(ActTypeNode.java:138)
        at
org.apache.cocoon.components.treeprocessor.AbstractParentProcessingNode.invokeNodes(AbstractParentProcessingNode.java:49)
        at
org.apache.cocoon.components.treeprocessor.sitemap.PreparableMatchNode.invoke(PreparableMatchNode.java:130)
        at
org.apache.cocoon.components.treeprocessor.AbstractParentProcessingNode.invokeNodes(AbstractParentProcessingNode.java:72)
        at
org.apache.cocoon.components.treeprocessor.sitemap.PipelineNode.invoke(PipelineNode.java:126)
        at
org.apache.cocoon.components.treeprocessor.AbstractParentProcessingNode.invokeNodes(AbstractParentProcessingNode.java:72)
        at
org.apache.cocoon.components.treeprocessor.sitemap.PipelinesNode.invoke(PipelinesNode.java:101)
        at
org.apache.cocoon.components.treeprocessor.TreeProcessor.process(TreeProcessor.java:336)
        at
org.apache.cocoon.components.treeprocessor.TreeProcessor.process(TreeProcessor.java:277)
        at
org.apache.cocoon.components.treeprocessor.sitemap.MountNode.invoke(MountNode.java:103)
        at
org.apache.cocoon.components.treeprocessor.AbstractParentProcessingNode.invokeNodes(AbstractParentProcessingNode.java:49)
        at
org.apache.cocoon.components.treeprocessor.sitemap.PreparableMatchNode.invoke(PreparableMatchNode.java:130)
        at
org.apache.cocoon.components.treeprocessor.AbstractParentProcessingNode.invokeNodes(AbstractParentProcessingNode.java:72)
        at
org.apache.cocoon.components.treeprocessor.sitemap.PipelineNode.invoke(PipelineNode.java:126)
        at
org.apache.cocoon.components.treeprocessor.AbstractParentProcessingNode.invokeNodes(AbstractParentProcessingNode.java:72)
        at
org.apache.cocoon.components.treeprocessor.sitemap.PipelinesNode.invoke(PipelinesNode.java:101)
        at
org.apache.cocoon.components.treeprocessor.TreeProcessor.process(TreeProcessor.java:336)
        at
org.apache.cocoon.components.treeprocessor.TreeProcessor.process(TreeProcessor.java:277)
        at org.apache.cocoon.Cocoon.process(Cocoon.java:639)
        at 
org.apache.cocoon.servlet.CocoonServlet.service(CocoonServlet.java:1098)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:810)
        at
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:237)
        at
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:157)
        at
org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:214)
        at
org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)
        at 
org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)
        at
org.apache.catalina.core.StandardContextValve.invokeInternal(StandardContextValve.java:198)
        at
org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:152)
        at
org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)
        at 
org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)
        at
org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:137)
        at
org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)
        at
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:117)
        at
org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:102)
        at 
org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)
        at
org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
        at
org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)
        at 
org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)
        at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:929)
        at 
org.apache.coyote.tomcat5.CoyoteAdapter.service(CoyoteAdapter.java:160)
        at 
org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:793)
        at
org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.processConnection(Http11Protocol.java:702)
        at 
org.apache.tomcat.util.net.TcpWorkerThread.runIt(PoolTcpEndpoint.java:571)
        at
org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:644)
        at java.lang.Thread.run(Thread.java:536)
Caused by: java.lang.IllegalArgumentException: type 12 is not a valid type
        at org.exist.xquery.value.Type.subTypeOf(Type.java:305)
        at org.exist.xquery.GeneralComparison.eval(GeneralComparison.java:131)
        at org.exist.xquery.AbstractExpression.eval(AbstractExpression.java:39)
        at org.exist.xquery.PathExpr.eval(PathExpr.java:118)
        at org.exist.xquery.Predicate.evalPredicate(Predicate.java:86)
        at org.exist.xquery.LocationStep.applyPredicate(LocationStep.java:98)
        at org.exist.xquery.LocationStep.eval(LocationStep.java:179)
        at org.exist.xquery.AbstractExpression.eval(AbstractExpression.java:39)
        at org.exist.xquery.PathExpr.eval(PathExpr.java:118)
        at 
org.exist.xquery.functions.util.EvalFunction.eval(EvalFunction.java:119)
        at org.exist.xquery.PathExpr.eval(PathExpr.java:100)
        at org.exist.xquery.LetExpr.eval(LetExpr.java:51)
        at org.exist.xquery.BindingExpression.eval(BindingExpression.java:97)
        at org.exist.xquery.AbstractExpression.eval(AbstractExpression.java:39)
        at org.exist.xquery.PathExpr.eval(PathExpr.java:118)
        at 
org.exist.xquery.UserDefinedFunction.eval(UserDefinedFunction.java:84)
        at org.exist.xquery.DynamicTypeCheck.eval(DynamicTypeCheck.java:53)
        at org.exist.xquery.FunctionCall.eval(FunctionCall.java:109)
        at org.exist.xquery.PathExpr.eval(PathExpr.java:100)
        at org.exist.xquery.EnclosedExpr.eval(EnclosedExpr.java:56)
        at org.exist.xquery.PathExpr.eval(PathExpr.java:100)
        at org.exist.xquery.ElementConstructor.eval(ElementConstructor.java:107)
        at org.exist.xquery.AbstractExpression.eval(AbstractExpression.java:39)
        at org.exist.xquery.PathExpr.eval(PathExpr.java:118)
        at org.exist.xquery.AbstractExpression.eval(AbstractExpression.java:39)
        at org.exist.xquery.LetExpr.eval(LetExpr.java:78)
        at org.exist.xquery.LetExpr.eval(LetExpr.java:76)
        at org.exist.xquery.LetExpr.eval(LetExpr.java:76)
        at org.exist.xquery.LetExpr.eval(LetExpr.java:76)
        at org.exist.xquery.LetExpr.eval(LetExpr.java:76)
        at org.exist.xquery.LetExpr.eval(LetExpr.java:76)
        at org.exist.xquery.BindingExpression.eval(BindingExpression.java:97)
        at org.exist.xquery.AbstractExpression.eval(AbstractExpression.java:39)
        at org.exist.xquery.PathExpr.eval(PathExpr.java:118)
        at
org.exist.xmldb.LocalXPathQueryService.doQuery(LocalXPathQueryService.java:240)
        at
org.exist.xmldb.LocalXPathQueryService.execute(LocalXPathQueryService.java:154)
        at org.exist.cocoon.XQueryGenerator.generate(XQueryGenerator.java:190)
        at
org.apache.cocoon.components.pipeline.AbstractProcessingPipeline.processXMLPipeline(AbstractProcessingPipeline.java:530)
        ... 59 more



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