I am using JBOSS 5.1 with Postgres 9.1
In my -ds.xml I put "normally"
JBOSS <type-mapping>PostgreSQL 9.1</type-mapping>
this caused :
ERROR [org.jboss.ejb.txtimer.GeneralPurposeDatabasePersistencePlugin.createTableIfNotExists:155] Cannot create timer table
java.lang.IllegalStateException: Cannot obtain type mapping from: jboss.jdbc:datasource=DefaultDS,service=metadata
I changed to JBOSS <type-mapping>PostgreSQL 8.0</type-mapping>
and the reoor diappeared.
So Peter Johnson was right.
Best