Share 'squash problems'

Hello fellow back yard gardeners! I have several varieties of squash, zuchinni, yellow crookneck and straight necks. I am haveing a problem with the fruits not developing propery. I get a female bloom, the squash develpoes about 3 inches, then the blossom end puckers, and the fruit withers. I am getting some to develpoe properly, but only about half. Any suggestions? The vines look great.