Opening database with PGACCESS

When I try to open my database (mydb) with the pgaccess, I receive the
following message:

"Error connecting database. Connection to database failed
connectDB() failed: Is the postmaster running and accepting
TCP/IP (with -i) connections at 'localhost' on port '5432'"

The postmaster is running and I can connect to mydb using "psql":

> psql mydb

"Welcome to the POSTGRESQL interactive sql monitor:
Please read the file COPYRIGHT for copyright terms of POSTGRESQL

type \? for help on slash commands
type \q to quit
type \g or terminate with semicolon to execute query
You are currently connected to the database: mydb

mydb=> "

Which is the problem? How can I fix it?

Thanks,

Rodney.