Yes, I've noticed that windows file sharing tends to be shaky at best. When first getting it hooked up right, it refuses to work, or has odd problems like you described. Then suddenly, it fixes itself and you never have problems again, at least until you unplug the cable for whatever reason. Then sometimes, the problems come up again. It's very odd.

Usually, to fix those problems I just shut down all the involved computers and turn them on again at the same time. Usually it works, sometimes it doesn't. *shrug*