When an XML syntax error is present in the persistence.xml file a parser exception is thrown that explains the error but as you can see in the source of JDOPersistenceManagerFactory.java below, that useful information in the exception is ignored and a new exception is thrown saying that the persistence unit could not be found - which is true but not as useful as conveying the reason why it could not be found:

                try
                {
                    // Obtain any props defined for the persistence-unit
                    pumd = nucleusContext.getMetaDataManager().getMetaDataForPersistenceUnit(persistenceUnitName);
                    if (pumd != null)
                    {
                        // Add the properties for the unit
                        if (pumd.getProperties() != null)
                        {
                            pmfProps.putAll(pumd.getProperties());
                        }
                    }
                    else
                    {
                        throw new JDOUserException(LOCALISER.msg("012004", persistenceUnitName));
                    }
                }
                catch (NucleusException jpe)
                {
                    throw new JDOUserException(LOCALISER.msg("012005", persistenceUnitName));
                }