If you're having this exception after updating a Rails application to version >=3.2.X, on Ruby >1.9.X..
uninitialized constant ActiveSupport::SecureRandom
..and you don't want to debug half dozen gems until you find which one is causing the error, you can use this hack as Ruby's >1.9 SecureRandom API is 100% compatible with the Rails <3.2 ActiveSupport::SecureRandom API.
Just add this line in some initializer:
ActiveSupport::SecureRandom = SecureRandom
This is absolute uglyness, but it works and I won't tell nobody that you went so lazy to use it ;-)