Ruby Script Transformation bug time to time

[MadOoor]

Sometimes, when I launch a transformation in kettle (V4.2.1 or V4.2.0) , everything works fine.
but other time (three times on Five), I got the following message. I don't know what to do :( please help me

2012/03/02 11:42:14 - Insert And Update.0 - ERROR (version 4.2.0-stable, build 15748 from 2011-09-08 13.11.42 by buildguy) : Unexpected error
2012/03/02 11:42:14 - Insert And Update.0 - ERROR (version 4.2.0-stable, build 15748 from 2011-09-08 13.11.42 by buildguy) : org.pentaho.di.core.exception.KettleException:
2012/03/02 11:42:14 - Insert And Update.0 - ERROR (version 4.2.0-stable, build 15748 from 2011-09-08 13.11.42 by buildguy) : org.jruby.embed.EvalFailedException: (NoMethodError) undefined method []' for true:TrueClass 2012/03/02 11:42:14 - Insert And Update.0 - ERROR (version 4.2.0-stable, build 15748 from 2011-09-08 13.11.42 by buildguy) : (NoMethodError) undefined method[]' for true:TrueClass
2012/03/02 11:42:14 - Insert And Update.0 - ERROR (version 4.2.0-stable, build 15748 from 2011-09-08 13.11.42 by buildguy) :
2012/03/02 11:42:14 - Insert And Update.0 - ERROR (version 4.2.0-stable, build 15748 from 2011-09-08 13.11.42 by buildguy) : at org.typeexit.kettle.plugin.steps.ruby.execmodels.SimpleExecutionModel.onProcessRow(SimpleExecutionModel.java:575)
2012/03/02 11:42:14 - Insert And Update.0 - ERROR (version 4.2.0-stable, build 15748 from 2011-09-08 13.11.42 by buildguy) : at org.typeexit.kettle.plugin.steps.ruby.RubyStep.processRow(RubyStep.java:32)
2012/03/02 11:42:14 - Insert And Update.0 - ERROR (version 4.2.0-stable, build 15748 from 2011-09-08 13.11.42 by buildguy) : at org.pentaho.di.trans.step.RunThread.run(RunThread.java:40)
2012/03/02 11:42:14 - Insert And Update.0 - ERROR (version 4.2.0-stable, build 15748 from 2011-09-08 13.11.42 by buildguy) : at java.lang.Thread.run(Thread.java:722)
2012/03/02 11:42:14 - Insert And Update.0 - ERROR (version 4.2.0-stable, build 15748 from 2011-09-08 13.11.42 by buildguy) : Caused by: org.jruby.embed.EvalFailedException: (NoMethodError) undefined method []' for true:TrueClass 2012/03/02 11:42:14 - Insert And Update.0 - ERROR (version 4.2.0-stable, build 15748 from 2011-09-08 13.11.42 by buildguy) : at org.jruby.embed.internal.EmbedEvalUnitImpl.run(EmbedEvalUnitImpl.java:127) 2012/03/02 11:42:14 - Insert And Update.0 - ERROR (version 4.2.0-stable, build 15748 from 2011-09-08 13.11.42 by buildguy) : at org.jruby.embed.ScriptingContainer.runUnit(ScriptingContainer.java:1231) 2012/03/02 11:42:14 - Insert And Update.0 - ERROR (version 4.2.0-stable, build 15748 from 2011-09-08 13.11.42 by buildguy) : at org.jruby.embed.ScriptingContainer.runScriptlet(ScriptingContainer.java:1247) 2012/03/02 11:42:14 - Insert And Update.0 - ERROR (version 4.2.0-stable, build 15748 from 2011-09-08 13.11.42 by buildguy) : at org.typeexit.kettle.plugin.steps.ruby.execmodels.SimpleExecutionModel.onProcessRow(SimpleExecutionModel.java:491) 2012/03/02 11:42:14 - Insert And Update.0 - ERROR (version 4.2.0-stable, build 15748 from 2011-09-08 13.11.42 by buildguy) : ... 3 more 2012/03/02 11:42:14 - Insert And Update.0 - ERROR (version 4.2.0-stable, build 15748 from 2011-09-08 13.11.42 by buildguy) : Caused by: org.jruby.exceptions.RaiseException: (NoMethodError) undefined method[]' for true:TrueClass