You're probably running into a naming issue. Models are expected to be the singular name and the tables will be plural as will the fixture files. You can see them all with the Pluralizer http://nubyonrails.com/tools/pluralize
But here's a simple listing:
class Feed < ActiveRecord::Base
in a database tables named "feeds"
It also expects to convert between CamelCase and under_scored so if your model is AggregationFeedMap, the file defining it should be app/models/aggregation_feed_map.rb and the table name should be aggregation_feed_maps and the fixture found in test/fixtures/aggregation_feed_maps.yml
Does this help you figure out your issues? It all becomes quite natural after a short while, but there are still times where you'll have a model name that the Inflector doesn't get the pluralization right and you either have to adjust or define an extra rule for the word you want to use.