SOLVED !!!
In first case the code is :
"If adval > 419 and adval < 536 then gosub LED" = working fine.
In second case :
"If adval > 450 and adval < 600 then gosub LED" = NOT working.

So I tried this :
"If adval < 600 and adval > 450 then gosub LED"
And VOILA, IT'S WORKING !!!

Thanks for support ! Regards !