You are trying to cache a Ruby object which cannot be serialized to memcached.

(dalli_memcache-client; rails3; ruby1.9; mongodb, Marshel).rb

Marshalling error for key '_my_session:1243f4a7a0c8d1dba363bc2ca7a246e8': singleton can't be dumped
You are trying to cache a Ruby object which cannot be serialized to memcached.
/usr/local/rvm/gems/ruby-1.9.3-p484/gems/dalli-2.7.0/lib/dalli/server.rb:398:in `dump'

#Controller problem
session[:telefones] = Cliente.telefones 

#Solution
session[:telefones] = Cliente.telefones.entries

# Monthpack: Global Solution
module Dalli
  class Server
    def serialize_with_modification(key, value, options=nil)
      serialize_without_modification(key, value.entries, options=nil)
    end
    alias_method_chain :serialize, :modification
  end
end

# Read the post: http://testandocomtesta.blogspot.com.br/2014/02/rails3-ruby19-dalli-memcache-client.html