it sounds like the big flaw was using VHS tapes, which was pretty much all that was available back then. As the tapes get worn down subjects might beinadvertantly cued that a certain segment was the target. Apparently there being more hits in later parts of trials gave weight to this or something.
Hopefully this link works:
Ganzfeld Experiment
Anyway, since 2000 everything has been computerized. Unfortunately the article doesn't specify how true to the ganzfeld protocol the 20 post-2000 studies have been so the results might not be as bad as they seem on the surface.