I forgot to give you some information : media used : VERBATIM DL, speed writing : 2,4, ISO image burning (so second layer switch strictly equal to original DVD.
The burned DVD can be read until the second layer sxitch (my interpretation !) but it's impossible to go to the second layer ; it's possible to reach chapters after the second layer switch.
Could you explain me the result of the test (i understand nothing !), give me some advice to improve.
Anyway, I would like to buy a better DVD burner able to wrute DBD DL ; what is now the best choice ?