you can't use this script on that way. Basically, this script is connect to one field, in your case listAtelierGraphique, am I right?
Then you need to use everything, validation, actionscript, before form pieces, begin submit (same as in documentation), and in form pieces, you can't use ff_getSubmit because this is for submit pieces.
For this you need select directly value from database, on the same way as it is described in documentation.
If you can give me access to this "#__specifictable", it would be great
I will see how to check this and let you know, please give me some time