If a file system task such as a rename fails, for example if the file does not exist, then this is considered an error by SSIS. This means the whole package fails. I can get aro
I know that this is an old question, but it might help someone looking for an answer.
Combined with user756519's quite good answer, stopping propagation of the error prevents the package from failing. This means that you can effectively use the failure as a branch without worrying about it mincing your package.
See cfrag's answer on this question for more information. That answer points to this blog entry which explains how to set the propagate variable for the OnError event handler (make the event handler, open variables view, show system variables, set Propogate to false).