Check that the extension of your DSN in the main.inc file is either pgsql or oci8. See the annotated main.inc file for more information.
If your database connection details look correct, it's most likely that PHP was not compiled with support for your database. See the MySource Matrix requirements for more information.
This usually means one of two things:
Your version on the Pear::DB module is deprecated. You should upgrade to the newest version of this module.
Consult the Java Console for any errors that might be occurring.