undefined method `named_scope' for #<Class:0x00000103606a90>

When adding as a gem for rails 3.1.1

The problem is in class preferences.rb line 163, 164

change
named_scope with scope

[ChristopheBelpaire]

This gem is not rails 3 compatible, there is a fork working with rails 3 :
https://github.com/rds/preferences