"postgresql-9.0-801.jdbc4.jar" Causing "Error committing transaction. Cause: org.postgresql.util.PSQLException: Cannot commit when autoCommit is enabled." Exception

Hello list,

. Postgresql8.3

. mybatis-3.0.5-SNAPSHOT.jar
. mybatis-spring-1.0.1-SNAPSHOT.jar
. spring3.0.5

. postgresql-9.0-801.jdbc4.jar


SqlSession sql_session = sqlSessionFactory.openSession(false);
....
sql_session.commit();



applicationContext-mybatis.xml

<bean id="dataSource"
class="org.springframework.jdbc.datasource.DriverManagerDataSource">
       <property name="driverClassName" value="${driverClassName}" />
       <property name="url"             value="${url}"      />
       <property name="username"        value="${username}" />
       <property name="password"        value="${password}" />
</bean>



When update/insert/delete is called, always got:
===================================================
### Error committing transaction.  Cause:
org.postgresql.util.PSQLException: Cannot commit when autoCommit is enabled.



While for "8.4-702 JDBC 4", the same codes, no error at all.

Is there anything need to be configured if using
"postgresql-9.0-801.jdbc4.jar"?

Thanks a lot!
Emi