"Protocol error. Session setup failed" (PostgreSQL 8.3devel/postgresql-8.3dev-600.jdbc3)

Hello,

I've built PostgreSQL 8.3 devel with VC++ 2005, done all the db
initialization process (creating the data dir using initdb, registering it
as a service using pg_ctl, etc) and tested by connecting to it through
pgAdmin III, I even built a C extension and ran it as a SP in the pgAdmin
SQL console.

I then restored a backup with the database of my under-development java
application in the hope that it would connect to this db transparently (I
have of course changed the jdbc driver to match the 8.3devel version).

When I tried to run my web java application, I received the following
PSQLException: ""Protocol error. Session setup failed"

What could be happening?

Note: I've attached the tomcat stack trace to the error.

Thanks,

Marcelo.