mongo_tail与正常的集合 Mongod 一起工作，但使用 Mongo 分析集合 system.profiling 时出现错误：
2014-01-10 11:53:37 +0700 [warn]: emit transaction failed error_class=NoMethodError error=#<NoMethodError: undefined method `to_msgpack' for 2014-01-10 03:14:13 UTC:Time>
2014-01-10 11:53:37 +0700 [warn]: /etc/td-agent/plugin/out_elasticsearch.rb:33:in `to_msgpack'
2014-01-10 11:53:37 +0700 [warn]: /etc/td-agent/plugin/out_elasticsearch.rb:33:in `to_msgpack'
2014-01-10 11:53:37 +0700 [warn]: /etc/td-agent/plugin/out_elasticsearch.rb:33:in `format'
2014-01-10 11:53:37 +0700 [warn]: /usr/lib64/fluent/ruby/lib/ruby/gems/1.9.1/gems/fluentd-0.10.41/lib/fluent/mixin.rb:96:in `block in format_stream'
2014-01-10 11:53:37 +0700 [warn]: /usr/lib64/fluent/ruby/lib/ruby/gems/1.9.1/gems/fluentd-0.10.41/lib/fluent/event.rb:54:in `call'
2014-01-10 11:53:37 +0700 [warn]: /usr/lib64/fluent/ruby/lib/ruby/gems/1.9.1/gems/fluentd-0.10.41/lib/fluent/event.rb:54:in `each'
2014-01-10 11:53:37 +0700 [warn]: /usr/lib64/fluent/ruby/lib/ruby/gems/1.9.1/gems/fluentd-0.10.41/lib/fluent/mixin.rb:93:in `format_stream'
2014-01-10 11:53:37 +0700 [warn]: /usr/lib64/fluent/ruby/lib/ruby/gems/1.9.1/gems/fluentd-0.10.41/lib/fluent/output.rb:235:in `emit'
2014-01-10 11:53:37 +0700 [warn]: /usr/lib64/fluent/ruby/lib/ruby/gems/1.9.1/gems/fluentd-0.10.41/lib/fluent/match.rb:36:in `emit'
2014-01-10 11:53:37 +0700 [warn]: /usr/lib64/fluent/ruby/lib/ruby/gems/1.9.1/gems/fluentd-0.10.41/lib/fluent/engine.rb:151:in `emit_stream'
2014-01-10 11:53:37 +0700 [warn]: /usr/lib64/fluent/ruby/lib/ruby/gems/1.9.1/gems/fluentd-0.10.41/lib/fluent/engine.rb:131:in `emit'
2014-01-10 11:53:37 +0700 [warn]: /usr/lib64/fluent/ruby/lib/ruby/gems/1.9.1/gems/fluent-plugin-mongo-0.7.1/lib/fluent/plugin/in_mongo_tail.rb:105:in `block in tailoop'
2014-01-10 11:53:37 +0700 [warn]: /usr/lib64/fluent/ruby/lib/ruby/gems/1.9.1/gems/fluent-plugin-mongo-0.7.1/lib/fluent/plugin/in_mongo_tail.rb:83:in `loop'
2014-01-10 11:53:37 +0700 [warn]: /usr/lib64/fluent/ruby/lib/ruby/gems/1.9.1/gems/fluent-plugin-mongo-0.7.1/lib/fluent/plugin/in_mongo_tail.rb:83:in `tailoop'
2014-01-10 11:53:37 +0700 [warn]: /usr/lib64/fluent/ruby/lib/ruby/gems/1.9.1/gems/fluent-plugin-mongo-0.7.1/lib/fluent/plugin/in_mongo_tail.rb:60:in `block in run'
2014-01-10 11:53:37 +0700 [warn]: /usr/lib64/fluent/ruby/lib/ruby/gems/1.9.1/gems/fluent-plugin-mongo-0.7.1/lib/fluent/plugin/in_mongo_tail.rb:59:in `loop'
2014-01-10 11:53:37 +0700 [warn]: /usr/lib64/fluent/ruby/lib/ruby/gems/1.9.1/gems/fluent-plugin-mongo-0.7.1/lib/fluent/plugin/in_mongo_tail.rb:59:in `run'
我该如何解决它，我想使用 fluent 将慢速 Mongodb 日志拉到其他地方。