77 blocks is very few. So, the only thing I'm left with is the fact if you scaled the textures or not. That is, if you set the scale of a texture to, say, 0.1, you'd have the equivelent of a single block being ten times bigger on all sides (a small 64x64 block would then become, in a sense, a 640x640 block, although only 64x64 quants in size). You shouldn't need to go below 0.25 and wouldn't recommend going below 0.5. Check your blocks for this sort of outrageous scaling you may have accidentally done. Also, flag the sides that cannot be seen (such as the undersides of floors) as "none", even in places where two walls of the same size (or the smaller one completely covered by a bigger one) meet up.