Ok, this bug (or these bugs) gets a bit annoying and we need to track it down. To help us tracking it, post how and when you got it and the last part of the critical error message (the stuff behind 'Assertion failed:') and the last, say 20 lines of your UT/DA2/System/DA2.log if you can obtain it.
Occured online to a friend of mine, while loading blackgold:
History: KInitSkeletonKarma <- KInitActorKarma <- AActor::setPhysics <- UObject::ProcessEvent <- (da_players_HumanPlayer DA2-BlackGold.da_players_HumanPlayer, Function XGame.xPawn.PlayDying) <- AActor::Tick <- TickAllActors <- ULevel::Tick <- (NetMode=3) <- TickLevel <- UGameEngine::Tick <- Level DA2 - BlackGold <- UpdateWorld <- MainLoop <- FMallocWindows::Free <- FMallocWindows::Realloc <- 676F4C57 0 FArray <- FArray::Realloc <- 0
...forgot to ask for the log-part, but this would go here.