Hibernate problem when building SessionFactory

I'm using Hibernate 3 with Oracle 10g Express and getting the following errors when inserting
new records in DB. The error only happens after serveral successful inserts.

Aug 22, 2007 8:53:52 PM org.hibernate.connection.DriverManagerConnectionProvider configure
INFO: Using Hibernate built-in connection pool (not for production use!)
Aug 22, 2007 8:53:52 PM org.hibernate.connection.DriverManagerConnectionProvider configure
INFO: Hibernate connection pool size: 10
Aug 22, 2007 8:53:52 PM org.hibernate.connection.DriverManagerConnectionProvider configure
INFO: autocommit mode: false
Aug 22, 2007 8:53:52 PM org.hibernate.connection.DriverManagerConnectionProvider configure
INFO: using driver: oracle.jdbc.driver.OracleDriver at URL: jdbc

racle:thin:@localhost:1521:XE
Aug 22, 2007 8:53:52 PM org.hibernate.connection.DriverManagerConnectionProvider configure
INFO: connection properties: {user=xyz, password=****}
Aug 22, 2007 8:53:52 PM org.hibernate.cfg.SettingsFactory buildSettings
WARNING: Could not obtain connection metadata
java.sql.SQLException: Listener refused the connection with the following error:
ORA-12519, TNS:no appropriate service handler found
The Connection descriptor used by the client was:
localhost:1521:XE

at oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:112)
at oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:261)
at oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:387)
at oracle.jdbc.driver.PhysicalConnection.<init>(PhysicalConnection.java:420)
at oracle.jdbc.driver.T4CConnection.<init>(T4CConnection.java:165)
at oracle.jdbc.driver.T4CDriverExtension.getConnection(T4CDriverExtension.java:35)
at oracle.jdbc.driver.OracleDriver.connect(OracleDriver.java:801)
at java.sql.DriverManager.getConnection(DriverManager.java:512)
at java.sql.DriverManager.getConnection(DriverManager.java:140)
at org.hibernate.connection.DriverManagerConnectionProvider.getConnection(DriverManagerConnectionProvider.java:110)
at org.hibernate.cfg.SettingsFactory.buildSettings(SettingsFactory.java:72)
at org.hibernate.cfg.Configuration.buildSettings(Configuration.java:1881)
at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1174)

ORA-12519, TNS:no appropriate service handler found

Looks like something to do with the services on the DB server.

Here's what the cause and action are for this error code.