Problem with db:create

My ruby app always created the databases on postgres just fine, but, a
days ago, I've tried to create a new project and when I execute the
command "db:create:all" i got the following error:

Couldn't create database for {"encoding"=>"unicode", "username"=> "-my
username-", "adapter"=>"postgresql",
"database"=>"argh_development", "host"=>"127.0.0.1", "pool"=>5,
"password"=>"-my password-"}
NoMethodError: undefined method `fformat' for #<PGresult:0xb6706be0>:
SHOW client_min_messages

What happens?

My database.yml is looking like this:

# PostgreSQL. Versions 7.4 and 8.x are supported.