could be a few things. you make it yourself? how? what material? did you charge it?
i've worked with many types of Ouija Boards, sometimes it's not purified, the people using it don't have enough energy, the spirit's too weak, or it's a design flaw. there's this one my friend bought for 70$ really gorgeous, made of marble and glass. the letters were written in Gothic print and it was held up by faeries. it's a lovely display piece, but it NEVER worked. mostly because no one, not even the spirits could read the letters.
you could of made it from wood that doesn't have deviation properties, or maybe it's not smooth enough for the planchette. try purifying and blessing it. then before using it, charge with energy.