Advise the client that an error has occurred

[Pierre-Luc Pineault]

Hello
Sorry for the bas english that follows
I use my own DefaultFtplet and i have redefine onUploadEnd(). In this method, i 
parse a file and if there is an error, the file is moved into an error file 
folder. This works perfectly but now, i want to advise the client that an error 
has occurred with his file (Incomplete, corrupted, ...).
How can i proceed ?
P-L