Ok, i had this problem too, and i found out that i can login only if i set the game to run on one or two cores only (task manager, find wows, right click, set affinity, and mark only cpu 1 and cpu 2, after that set priority to high) and after that i can normally login. As soon i revert changes i get disconnected, and cant login again untill i do the steps again. My cpu is AMD Phenom II X4 940.