When upgrade mongoid to 2.2.4, I accidentally updated mongo to 1.4.0 too, and there's many connection failures like following:

Mongo::ConnectionFailure
Error
Cannot connect to a replica set using seeds db1:27017
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongo-1.4.0/lib/../lib/mongo/util/pool_manager.rb:199:in `get_valid_seed_node'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongo-1.4.0/lib/../lib/mongo/util/pool_manager.rb:83:in `connect_to_members'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongo-1.4.0/lib/../lib/mongo/util/pool_manager.rb:25:in `connect'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongo-1.4.0/lib/../lib/mongo/repl_set_connection.rb:220:in `refresh'
/usr/local/rvm/rubies/ree-1.8.7-2011.03/lib/ruby/1.8/sync.rb:230:in `sync_synchronize'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongo-1.4.0/lib/../lib/mongo/repl_set_connection.rb:217:in `refresh'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongo-1.4.0/lib/../lib/mongo/repl_set_connection.rb:402:in `checkout_writer'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongo-1.4.0/lib/../lib/mongo/connection.rb:481:in `receive_message'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongo-1.4.0/lib/../lib/mongo/cursor.rb:464:in `send_initial_query'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongo-1.4.0/lib/../lib/mongo/util/logging.rb:23:in `instrument'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongo-1.4.0/lib/../lib/mongo/cursor.rb:463:in `send_initial_query'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongo-1.4.0/lib/../lib/mongo/cursor.rb:454:in `refresh'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongo-1.4.0/lib/../lib/mongo/cursor.rb:124:in `next_document'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongo-1.4.0/lib/../lib/mongo/collection.rb:287:in `find_one'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongoid-2.2.4/lib/mongoid/collections/master.rb:19:in `find_one'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongoid-2.2.4/lib/mongoid/collections/retry.rb:29:in `retry_on_connection_failure'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongoid-2.2.4/lib/mongoid/collections/master.rb:18:in `find_one'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongoid-2.2.4/lib/mongoid/collection.rb:60:in `find_one'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongoid-2.2.4/lib/mongoid/contexts/mongo.rb:164:in `one'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongoid-2.2.4/lib/mongoid/criteria.rb:43:in `_send_'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongoid-2.2.4/lib/mongoid/criteria.rb:43:in `one'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongoid-2.2.4/lib/mongoid/criterion/inclusion.rb:269:in `from_map_or_db'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongoid-2.2.4/lib/mongoid/criterion/inclusion.rb:250:in `execute_or_raise'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongoid-2.2.4/lib/mongoid/criterion/inclusion.rb:106:in `find'

====

Mongo::ConnectionFailure
Error
Could not connect to primary node.
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongo-1.4.0/lib/../lib/mongo/repl_set_connection.rb:409:in `checkout_writer'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongo-1.4.0/lib/../lib/mongo/connection.rb:481:in `receive_message'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongo-1.4.0/lib/../lib/mongo/cursor.rb:464:in `send_initial_query'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongo-1.4.0/lib/../lib/mongo/util/logging.rb:23:in `instrument'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongo-1.4.0/lib/../lib/mongo/cursor.rb:463:in `send_initial_query'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongo-1.4.0/lib/../lib/mongo/cursor.rb:454:in `refresh'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongo-1.4.0/lib/../lib/mongo/cursor.rb:124:in `next_document'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongo-1.4.0/lib/../lib/mongo/collection.rb:287:in `find_one'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongoid-2.2.4/lib/mongoid/collections/master.rb:19:in `find_one'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongoid-2.2.4/lib/mongoid/collections/retry.rb:29:in `retry_on_connection_failure'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongoid-2.2.4/lib/mongoid/collections/master.rb:18:in `find_one'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongoid-2.2.4/lib/mongoid/collection.rb:60:in `find_one'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongoid-2.2.4/lib/mongoid/contexts/mongo.rb:164:in `one'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongoid-2.2.4/lib/mongoid/criteria.rb:43:in `_send_'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongoid-2.2.4/lib/mongoid/criteria.rb:43:in `one'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongoid-2.2.4/lib/mongoid/criterion/inclusion.rb:269:in `from_map_or_db'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongoid-2.2.4/lib/mongoid/criterion/inclusion.rb:250:in `execute_or_raise'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongoid-2.2.4/lib/mongoid/criterion/inclusion.rb:106:in `find'
/usr/local/rvm/gems/ree-1.8.7-2011.03/gems/mongoid-2.2.4/lib/mongoid/finders.rb:83:in `find'

After reverting back to mongoid-2.2.4 + mongo-1.3.1 it works as before.