JavaEE 6: javax.naming.NameAlreadyBoundException: Use rebind to override

By default GlassFish Server specific default JNDI names are applied automatically for backward compatibility. So com.transbinary.imdb.service.UserManagementService is the the default JNDI name for both the implementations of UserManagementService interface. Which was why I was gettting javax.naming.NameAlreadyBoundException exception.

But because the EJB 3.1 specification defines portable EJB JNDI names, there is less need for GlassFish Server specific JNDI names.

To disable GlassFish Server specific JNDI names for an EJB module, set the value of disable-nonportable-jndi-names element to true. The default is false.

It solved the problem.

Resource: http://wikis.oracle.com/display/GlassFish/Developer+Handoff+to+QA+for+EJB-8+%28Option+to+disable+GlassFish-specific+JNDI%29

GlassFish restart. (It worked for me.)