Thanks a lot! I'll try it this night, and give you a reply if it works. During the day it is just not possible to "build all", it always stops while "calculating category stats". Maybe my host provider is too slow.

BTW: what is done with "calculating category stats"? Can one skip this or is it necessary? I also do not need the votes and the ratings, can I deactivate this in the building option (only if it is faster)?