curiously yesterday I deleted all the blocks code from the contrib directory (in part because it's now in moodle (main) directory and because I had some suspects about people using it instead of the "oficial" code).
It your CVS client is telling you that the blocks dir doesn't exist I think it's produced because your are trying to download it from contrib instead of moodle.
If this is your situation, please upgrade ALL your moodle dir to the latest one and try again. It should work.
Ciao