miwa's right, some problems are just down to genetics, i had a blue mystic about 12 months ago that was badly deformed and died at the 4th node, so i checked online and many growers where having the same problems, all the seeds came from the same breeder but i got mine from herbies, i told herbie and he pulled the seeds from sale as i think their was 3 people on this site having the same problems, 2 from heribes and 1 from attitude but all the seeds where from the same breeder, all our plants had the same genetic problem and all died at the 4th or 5th node, so i left the blue mystic for a while but herbie told me he got a really nice blue mystic strain a few weeks back so i ordered a few blue mystic seeds but not planted them yet,
so you cant rule out genetics, ive had plants that start deformed and by node 4 or 5 it usually grows out, but i dont use them plant for seed production as you dont want to pass that genetic on,
if you are sure the growing conditions are ok then it could just be a gentic problem, if the place you got the seeds from is able to discuss germination then let them know you have a problem and they may offer a replacement in your next order, you never know their may be other growers out their having similar problems, its got to be worth letting them know as a free seed in your next order is always a nice bonus