Did you level the ground first? Did you try to hoe the ground, or fertilize it? I've also seen squares that I could not plant on, but it's fairly rare.
When I start a garden/farm, I start out by laying down a layer of wood frames to level the ground. Then I remove them, hoe, and plant. Gives me 100% results that way, and I can harvest and replant without problems. YMMV