I just got it to work. The situation was that i was updating WOW, and i hadn't playing it in soooo long that the game had to download a huge amount of patches and updates. Well my WOW folder now is ~12Gb !.... So i excluded that from the Time Machine backup and it worked !
Nevertheless, the problem described above from the original post remains.
On another note, does WOW take that much space ? Or can i throw away all does "patch" and "downloader" files ?