In addition to Hawkwalk's good advice, you should mulch the base of the plant with peat moss or some other such material if you're experiencing dry weather. Even then, be sure to water every other day at least a total of an inch per week.
If the malady continues, you can try spraying with calcium chloride, but ever so lightly. You can also try a fairly high phosphate rich fertilizer, say 5-15-5 or even 5-20-5.
You may have planted them to early in cold soil. this is a common cause of th eblossom end rot. The soil temperature should be a minimum of 50 degrees F before transplanting... Best of luck!