We are seeing this error a few times a day. Other codes have been seen (e.g. 0, 45, 29, 78), but it's always the same stack trace. The refresh (defaulted to 90 sec) command when calling "ismaster". All Passenger threads will stop working until Apache is restarted.

...3/lib/ruby/gems/1.8/gems/bson-1.6.2/lib/bson/bson_c.rb: 28:in `deserialize'
...3/lib/ruby/gems/1.8/gems/bson-1.6.2/lib/bson/bson_c.rb: 28:in `deserialize'
...ruby/gems/1.8/gems/mongo-1.6.2/lib/mongo/networking.rb: 236:in `read_documents'
...ruby/gems/1.8/gems/mongo-1.6.2/lib/mongo/networking.rb: 177:in `receive'
...ruby/gems/1.8/gems/mongo-1.6.2/lib/mongo/networking.rb: 139:in `receive_message'
...lib/ruby/gems/1.8/gems/mongo-1.6.2/lib/mongo/cursor.rb: 469:in `send_initial_query'
...by/gems/1.8/gems/mongo-1.6.2/lib/mongo/util/logging.rb: 36:in `instrument_trace'
...20803221908/config/initializers/rpm_instrumentation.rb: 252:in `instrument'
...20803221908/config/initializers/rpm_instrumentation.rb: 250:in `instrument'
...lib/ruby/gems/1.8/gems/mongo-1.6.2/lib/mongo/cursor.rb: 467:in `send_initial_query'
...lib/ruby/gems/1.8/gems/mongo-1.6.2/lib/mongo/cursor.rb: 458:in `refresh'
...lib/ruby/gems/1.8/gems/mongo-1.6.2/lib/mongo/cursor.rb: 128:in `next_document'
....03/lib/ruby/gems/1.8/gems/mongo-1.6.2/lib/mongo/db.rb: 511:in `command'
.../ruby/gems/1.8/gems/mongo-1.6.2/lib/mongo/util/node.rb: 83:in `set_config'
...ms/1.8/gems/mongo-1.6.2/lib/mongo/util/pool_manager.rb: 126:in `validate_existing_member'
...ms/1.8/gems/mongo-1.6.2/lib/mongo/util/pool_manager.rb: 70:in `check_connection_health'
...ms/1.8/gems/mongo-1.6.2/lib/mongo/util/pool_manager.rb: 65:in `each'
...ms/1.8/gems/mongo-1.6.2/lib/mongo/util/pool_manager.rb: 65:in `check_connection_health'
.../1.8/gems/mongo-1.6.2/lib/mongo/repl_set_connection.rb: 185:in `refresh'
.../1.8/gems/mongo-1.6.2/lib/mongo/repl_set_connection.rb: 555:in `sync_refresh'
.../1.8/gems/mongo-1.6.2/lib/mongo/repl_set_connection.rb: 311:in `checkout'
.../1.8/gems/mongo-1.6.2/lib/mongo/repl_set_connection.rb: 368:in `checkout_writer'
...ruby/gems/1.8/gems/mongo-1.6.2/lib/mongo/networking.rb: 34:in `send_message'
...ruby/gems/1.8/gems/mongo-1.6.2/lib/mongo/collection.rb: 443:in `update'