Which application server are you using ?
I have this error when I use Jboss AS 5.1 and set hibernate.hbm2ddl.auto to create in ther persistance.xml file, this create the data base the first time
if it's your case u need to remove this line from the file :
<property name="hibernate.hbm2ddl.auto" value="create" />
or not use the jboss transaction manager
hope this will help