I am using Rails 3.0.3 and got this error :
couldn't parse YAML at line 182 column 9 (Psych::SyntaxError)
As I understand it, there is an issue with the locale file (locale/en.yml) of ActiveSupport.
Just by adding
require 'yaml'
YAML::ENGINE.yamler= 'syck'
at the beginning of the boot.rb file should take care of this issue.