I have just finished doing something similar like you. From flat file source, grab the failure precedent constraint (red arrow) and put it in a script task transformation. Then configure the task and in script click design script and add this script there:
Row.ErrorDescription = ComponentMetaData.GetErrorDescription(Row.ErrorCode)
Then to a destination of your choice!!!!!
[font="Verdana"]Imagination is more important than knowledge-Albert Einstein[/font]