Can't connect Datamapper with PostgreSQL under Windows - ruby

Question

I'm just trying to make a connection, but I keep getting some errors
This is my code:
require 'data_mapper'
# A Postgres connection:
DataMapper.setup(:default, 'postgres://postgres:mypassword#localhost:5432/pruebas')
And these are the errors:
C:/Ruby193/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36:in `require':
126: No se puede encontrar el módulo especificado. - C:/Ruby193/lib/ruby/gems/
1.9.1/gems/do_postgres-0.10.10-x86-mingw32/lib/do_postgres/1.9/do_postgres.so (L
oadError)
from C:/Ruby193/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36:i
n `require'
from C:/Ruby193/lib/ruby/gems/1.9.1/gems/do_postgres-0.10.10-x86-mingw32
/lib/do_postgres.rb:30:in `rescue in <top (required)>'
from C:/Ruby193/lib/ruby/gems/1.9.1/gems/do_postgres-0.10.10-x86-mingw32
/lib/do_postgres.rb:25:in `<top (required)>'
from C:/Ruby193/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36:i
n `require'
from C:/Ruby193/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36:i
n `require'
from C:/Ruby193/lib/ruby/gems/1.9.1/gems/dm-postgres-adapter-1.2.0/lib/d
m-postgres-adapter/adapter.rb:1:in `<top (required)>'
from C:/Ruby193/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36:i
n `require'
from C:/Ruby193/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36:i
n `require'
from C:/Ruby193/lib/ruby/gems/1.9.1/gems/dm-postgres-adapter-1.2.0/lib/d
m-postgres-adapter.rb:1:in `<top (required)>'
from C:/Ruby193/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:60:i
n `require'
from C:/Ruby193/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:60:i
n `rescue in require'
from C:/Ruby193/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:35:i
n `require'
from C:/Ruby193/lib/ruby/gems/1.9.1/gems/dm-core-1.2.0/lib/dm-core/adapt
ers.rb:163:in `load_adapter'
from C:/Ruby193/lib/ruby/gems/1.9.1/gems/dm-core-1.2.0/lib/dm-core/adapt
ers.rb:133:in `adapter_class'
from C:/Ruby193/lib/ruby/gems/1.9.1/gems/dm-core-1.2.0/lib/dm-core/adapt
ers.rb:13:in `new'
from C:/Ruby193/lib/ruby/gems/1.9.1/gems/dm-core-1.2.0/lib/dm-core.rb:23
0:in `setup'
from pruebadb.rb:4:in `<main>'
Translation for No se puede encontrar el módulo especificado. : Cannot find the specified module.
I've googled a lot with no answer.