Hibernate version:
Hibernate 2.1.4
Hibernate-ext 2.1.3

Full stack trace of any exception that occurs:
/home/bart/data/workspace/Time/build.xml:55: Schema text failed: Could not instantiate dialect class
at net.sf.hibernate.tool.hbm2ddl.SchemaExportTask.execute(SchemaExportTask.java:146)
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.executeTarget(Project.java:1214)
at org.apache.tools.ant.Project.executeTargets(Project.java:1062)
at org.apache.tools.ant.Main.runBuild(Main.java:673)
at org.apache.tools.ant.Main.startAnt(Main.java:188)
at org.apache.tools.ant.launch.Launcher.run(Launcher.java:196)
at org.apache.tools.ant.launch.Launcher.main(Launcher.java:55)
Caused by: net.sf.hibernate.HibernateException: Could not instantiate dialect class
at net.sf.hibernate.dialect.Dialect.getDialect(Dialect.java:383)
at net.sf.hibernate.tool.hbm2ddl.SchemaExport.<init>(SchemaExport.java:57)
at net.sf.hibernate.tool.hbm2ddl.SchemaExportTask.getSchemaExport(SchemaExportTask.java:209)
at net.sf.hibernate.tool.hbm2ddl.SchemaExportTask.execute(SchemaExportTask.java:136)
... 10 more
Caused by: java.lang.ClassCastException
at net.sf.hibernate.dialect.Dialect.getDialect(Dialect.java:377)
... 13 more
--- Nested Exception ---
net.sf.hibernate.HibernateException: Could not instantiate dialect class
at net.sf.hibernate.dialect.Dialect.getDialect(Dialect.java:383)
at net.sf.hibernate.tool.hbm2ddl.SchemaExport.<init>(SchemaExport.java:57)
at net.sf.hibernate.tool.hbm2ddl.SchemaExportTask.getSchemaExport(SchemaExportTask.java:209)
at net.sf.hibernate.tool.hbm2ddl.SchemaExportTask.execute(SchemaExportTask.java:136)
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.executeTarget(Project.java:1214)
at org.apache.tools.ant.Project.executeTargets(Project.java:1062)
at org.apache.tools.ant.Main.runBuild(Main.java:673)
at org.apache.tools.ant.Main.startAnt(Main.java:188)
at org.apache.tools.ant.launch.Launcher.run(Launcher.java:196)
at org.apache.tools.ant.launch.Launcher.main(Launcher.java:55)
Caused by: java.lang.ClassCastException
at net.sf.hibernate.dialect.Dialect.getDialect(Dialect.java:377)
... 13 more

Name and version of the database you are using:
Postgres 7.4.6 with jdbc3-postgresql

Debug level Hibernate log excerpt:
[schemaexport] INFO - Hibernate 2.1.4
[schemaexport] INFO - loaded properties from resource hibernate.properties: {hibernate.connection.username=bart, hibernate.connection.password=, hibernate.cglib.use_reflection_optimizer=true, hibernate.dialect=net.sf.hibernate.dialect.PostgreSQLDialect, hibernate.connection.url=jdbc:postgresql://localhost/example, hibernate.connection.driver_class=org.postgresql.Driver}
[schemaexport] INFO - using CGLIB reflection optimizer
[schemaexport] INFO - Mapping file: /home/bart/data/workspace/Time/classes/com/om/Time/User.hbm.xml
[schemaexport] DEBUG - trying to locate http://hibernate.sourceforge.net/hibern ... ng-2.0.dtd in classpath under net/sf/hibernate/
[schemaexport] DEBUG - found http://hibernate.sourceforge.net/hibern ... ng-2.0.dtd in classpath
[schemaexport] INFO - Mapping class: com.om.Time.User -> users
[schemaexport] DEBUG - Mapped property: id -> id, type: long
[schemaexport] DEBUG - Mapped property: name -> name, type: string
[schemaexport] INFO - Using dialect: net.sf.hibernate.dialect.PostgreSQLDialect

BUILD FAILED
/home/bart/data/workspace/Time/build.xml:55: Schema text failed: Could not instantiate dialect class


User.hbml.xml
.. xml info here
<hibernate-mapping>
<class name="com.om.Time.User" table="users">
<id name="id" column="id" type="long">
<generator class="sequence">
<param name="sequence">id_sequence</param>
</generator>
</id>
<property name="name" column="name" type="string"/>
</class>
</hibernate-mapping>

Comment
First of all i am a java newbie. I followed a tutorial in James Elliott's "Developer Notebook" and run into this error. I tried also change the dialect to MySQL or Sybase, nothing worked.

Please, put me in the right direction.

Thanks Bart