Kitava Crashes

i am in act 5 and tried last night and now today to kill kitava in act5 even with help of others but after kitava turns red after the first staff of purity beam my game crashes immediately. even if i come in later after another guy is killing it my game crashes immediately. cant progress past act 5

also the map Belfry on the rooftop with kitava crashes after beam just like the act 5 boss.