NoMethodError: undefined method allocate using Twilio and MongoMapper

I am trying to use twilio (http://ift.tt/1q7fNM4) in an app I am working on. The problem is, when I install it (using bundler) one of my models throws:

"NoMethodError: undefined method `allocate' for Builder:Module" 

on my model. I can't tell where this error is even coming from. What could be causing this?

I am using:

gem 'twilio-ruby', '~> 4.11.1'
gem 'rails', '3.2.11'
gem 'mongo_mapper', '0.12.0'

Here is the trace for a call on the collection using first:

NoMethodError: undefined method `allocate' for Builder:Module
    from SYSTEM/ruby-1.9.3-p448@PROJECT/gems/mongo_mapper-0.12.0/lib/mongo_mapper/plugins/keys.rb:63:in `load'
    from SYSTEM/ruby-1.9.3-p448@PROJECT/gems/mongo_mapper-0.12.0/lib/mongo_mapper/plugins/identity_map.rb:104:in `load'
    from SYSTEM/ruby-1.9.3-p448@PROJECT/gems/mongo_mapper-0.12.0/lib/mongo_mapper/plugins/querying.rb:76:in `block in transformer'
    from SYSTEM/ruby-1.9.3-p448@PROJECT/gems/mongo-1.12.3/lib/mongo/cursor.rb:168:in `call'
    from SYSTEM/ruby-1.9.3-p448@PROJECT/gems/mongo-1.12.3/lib/mongo/cursor.rb:168:in `next'
    from SYSTEM/ruby-1.9.3-p448@PROJECT/gems/mongo-1.12.3/lib/mongo/collection.rb:329:in `find_one'
    from SYSTEM/ruby-1.9.3-p448@PROJECT/gems/plucky-0.5.2/lib/plucky/query.rb:69:in `find_one'
    from SYSTEM/ruby-1.9.3-p448@PROJECT/gems/mongo_mapper-0.12.0/lib/mongo_mapper/plugins/identity_map.rb:74:in `find_one'
    from SYSTEM/ruby-1.9.3-p448@PROJECT/gems/plucky-0.5.2/lib/plucky/query.rb:86:in `first'
    from (irb):19
    from SYSTEM/ruby-1.9.3-p448@PROJECT/gems/railties-3.2.11/lib/rails/commands/console.rb:47:in `start'
    from SYSTEM/ruby-1.9.3-p448@PROJECT/gems/railties-3.2.11/lib/rails/commands/console.rb:8:in `start'
    from SYSTEM/ruby-1.9.3-p448@PROJECT/gems/railties-3.2.11/lib/rails/commands.rb:41:in `<top (required)>'
    from script/rails:6:in `require'
    from script/rails:6:in `<main>'