getting IDENT authentication failed error

Hi all. I've successfully created a user "unbc", and am attempting to create a database with the following:

createdb -U unbc -W -e unbc

but I get this error message:

psql: FATAL 1: IDENT authentication faild for user "unbc"

If I create the database with no password,

createdb -e unbc

it works fine.

I'm searching through google but am not having much luck. Can anyone give any advice as to what is causing this error?

Thanks in advance,

Pablo