If the postgreSQL database is on the same machine as your web container running Geoportal Server, you might want to try:
# IPv4 local connections:
host all all 127.0.0.1/32 trust
(That's how mine is set up)
Still, it is probably worth double checking the following:
[ ] You can connect to your database using pgAdmin
[ ] The postgresql jdbc driver matches the version level of your postgreSQL database
[ ] The url value for the JNDI context file is pointing to the right postgreSQL database