I am answering myself in case it interests someone. I have finally solved
this after two days of wasting my time. I am not very happy with the book
"Client/Server programming with Java and Corba 2.ed", since it seems to have
upgraded the code without having upgraded the software. I obviously had
an old edition of the file vbjorb.jar. Fortunately I finally found out that
this file also follows Oracle installations, and that I had a newer version
in my Oracle folder. I copied it over, and voila, problem solved.