During a characters A turn (when he is about to roll a die in battle) character B cast the misfortune spell (character automatically rolls a 1) on character A....

Now, can the character A cast the magic shell?? "cast on yourself at the start or end of your turn. No spells or magic objects will effect you until the start of your next turn"

Now, i belive that character A can`t cast this spell to neget the misfortune spell, since it`s not in the beginning or the end of his turn.... what do you think?

You are already in the battle phase, so magic shell can only be cast at the end of your turn or in your next turn etc

On top of that, misfortune has already been cast, so he can do nothing about it, except if he has the counter or reflection spell.

(It's bad luck for player A