what's no pbkey error

[Johnson]

I try to bind the registration example to database by OJB JDO. my database is postgres,had primary key setup ok,every thing seemed right. But when I test it,the system has a error below,   "file:/jakarta-tomcat-5.0.18/webapps/cocoon/test/flow/registration.js", line 8: uncaught _javascript_ exception: at registration (file:/jakarta-tomcat-5.0.18/webapps/cocoon/test/flow/registration.js, Line 8): org.apache.ojb.broker.PBFactoryException: There was no default-PBKey specified what's this. Best Regards Johnson