RemoteException "Failed to index an event, will retry"


We are using Logstash to feed a clustered ES with log data. Everything works fine, but for a specific log file we are getting hammered with "RemoteTransportException" exceptions in the logstash log, e.g.

{:timestamp=>"2013-09-13T09:13:30.445000+0200", :message=>"Failed to index an event, will retry", :exception=>org.elasticsearch.transport.RemoteTransportException: [Strong Guy][inet[/]][index],

Any ideas why this happens? Or how we can find out what is causing the error? The ES status is green and no errors in the ES logs