Problema con Active Record

Hola gente!!

Es la primera vez que posteo en esta lista, por lo que un cordial
saludo a todos!!

Por otra parte, estoy atascado en un problemilla de ActiveRecord, que
al ejecutar los tests me dice que

/usr/lib/ruby/gems/1.8/gems/activerecord-1.14.4/lib/active_record/associations.rb:1064:in
create_belongs_to_reflection': undefined methodassert_valid_keys’
for :trainer:Symbol (NoMethodError)
from
/usr/lib/ruby/gems/1.8/gems/activerecord-1.14.4/lib/active_record/associations.rb:647:in
belongs_to' from /home/eneko/radrails/xfutbol/config/../app/models/contract.rb:2 from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:27:inrequire’
from
/usr/lib/ruby/gems/1.8/gems/activesupport-1.3.1/lib/active_support/dependencies.rb:147:in
require' from /usr/lib/ruby/gems/1.8/gems/activerecord-1.14.4/lib/active_record/fixtures.rb:463:inrequire_fixture_classes’
from
/usr/lib/ruby/gems/1.8/gems/activerecord-1.14.4/lib/active_record/fixtures.rb:459:in
require_fixture_classes' from /usr/lib/ruby/gems/1.8/gems/activerecord-1.14.4/lib/active_record/fixtures.rb:454:infixtures’
from test/unit/player_test.rb:5

sabeis qué es lo que puede ser ese error de assert_valid_keys??

Es dificíl sin ver el modelo y la base de datos, que tienes en
contract.rb?