logstash - invalid byte sequence in UTF-8

gistfile1.rb

{
  :timestamp=>"2014-04-24T11:09:00.344000+0000", 
  :message=>"Exception in filterworker", 
    "exception"=>#<ArgumentError: invalid byte sequence in UTF-8>, 
    "backtrace"=>[
      "org/jruby/RubyRegexp.java:1674:in `=~'", 
      "(eval):234:in `initialize'", 
      "org/jruby/RubyProc.java:271:in `call'", 
      "/opt/logstash/lib/logstash/pipeline.rb:262:in `filter'", 
      "/opt/logstash/lib/logstash/pipeline.rb:203:in `filterworker'", 
      "/opt/logstash/lib/logstash/pipeline.rb:143:in `start_filters'"], 
  :level=>:error
  }