My bad,
I removes all ressources the script was loading , because these ressources (pics, sounds) are not part of LE3 package,
and i had no problem with camera using the two versions :
Script.Camera = "" --entity
Script.Camera = nil --entity
The error message was not precise and mislead me to think it was that line the problem, but in fact it was ressources not loaded and used in script it seems.
The thread can be closed