block loading on single player

when i start a single player world and start exploring it says that the blocks under my feet are invisable but are still there but cannot be seen and the only way to fix is by changing some video settings or reloading the world but if i go exploring more then more invisable blocks pop up its always like a whole chunk thats invisable not just one block but yeah i hope it has nothing to do with my PC im pretty sure its the snapshot though because i am find on 1.7.4
good luck with everything.