Stack traces are ugly and informative, like this ...
Code:
org.hibernate.MappingException: Could not read mapping document from file: D:\workspace-hibtools3\Demo\ce\org\hibernate\auction\Bid.hbm.xml
   at org.hibernate.cfg.Configuration.addFile(Configuration.java:264)
   at org.hibernate.tool.ant.ConfigurationTask.addFile(ConfigurationTask.java:140)
   at org.hibernate.tool.ant.ConfigurationTask.addMappings(ConfigurationTask.java:123)
   at org.hibernate.tool.ant.ConfigurationTask.doConfiguration(ConfigurationTask.java:109)
   at org.hibernate.tool.ant.ConfigurationTask.getConfiguration(ConfigurationTask.java:55)
   at org.hibernate.tool.ant.HibernateToolTask.getConfiguration(HibernateToolTask.java:180)
   at org.hibernate.tool.ant.HibernateToolTask.getProperties(HibernateToolTask.java:196)
   at org.hibernate.tool.ant.ExporterTask.configureExporter(ExporterTask.java:90)
   at org.hibernate.tool.ant.Hbm2JavaGeneratorTask.configureExporter(Hbm2JavaGeneratorTask.java:37)
   at org.hibernate.tool.ant.ExporterTask.execute(ExporterTask.java:38)
   at org.hibernate.tool.ant.HibernateToolTask.execute(HibernateToolTask.java:144)
   at org.apache.tools.ant.UnknownElement.execute(UnknownElement.java:275)
   at org.apache.tools.ant.Task.perform(Task.java:364)
   at org.apache.tools.ant.Target.execute(Target.java:341)
   at org.apache.tools.ant.Target.performTasks(Target.java:369)
   at org.apache.tools.ant.Project.executeSortedTargets(Project.java:1216)
   at org.apache.tools.ant.Project.executeTarget(Project.java:1185)
   at org.apache.tools.ant.helper.DefaultExecutor.executeTargets(DefaultExecutor.java:40)
   at org.apache.tools.ant.Project.executeTargets(Project.java:1068)
   at org.eclipse.ant.internal.ui.antsupport.InternalAntRunner.run(InternalAntRunner.java:416)
   at org.eclipse.ant.internal.ui.antsupport.InternalAntRunner.main(InternalAntRunner.java:138)
Caused by: org.hibernate.MappingException: Unable to determine entity name
   at org.hibernate.cfg.HbmBinder.bindClass(HbmBinder.java:484)
   at org.hibernate.cfg.HbmBinder.bindRootClass(HbmBinder.java:236)
   at org.hibernate.cfg.HbmBinder.bindRoot(HbmBinder.java:109)
   at org.hibernate.cfg.Configuration.add(Configuration.java:380)
   at org.hibernate.cfg.Configuration.addInputStream(Configuration.java:419)
   at org.hibernate.cfg.Configuration.addFile(Configuration.java:261)
   ... 20 more