Role Authentication Failure

I can't understand what is going on with my PostgreSQL server. For
some reason after I GRANT my role 'carlos' to the 'dba' group role, I
lose the ability to login. I've reset the password over and over for
'carlos' and even reversing the grant doesn't remedy the
authentication failure. The logs are extremely vague:

2013-04-14 00:41:52 EDT FATAL: password authentication failed for user "carlos"

My roles look as follows:

postgres=# \dg
List of roles
Role name | Attributes | Member of
-----------+------------------------------------------------+-----------
carlos | Superuser, Create role, Create DB, Replication | {}
dba | No inheritance, Cannot login | {}
postgres | Superuser, Create role, Create DB, Replication | {}

As you can see I've removed 'dba' role from 'carlos' but he still
can't login. My only option is to DROP the 'carlos' role and re-create
him.

The problem occurs when I:

GRANT dba TO carlos;

I don't understand which role (carlos or dba) needs INHERIT or
NOINHERIT if that's causing this...

--
Carlos Mennens