Is your tester just that, a tester? or is a full programmer? If it is just a tester, can you do a reflash from the computer? Maybe the programming got corrupted or something. If it is a programmer and you have your car tuned, then that might cause a problem doing that.
You could always take the car to pepboys or something and have them hook up to your car with there tester. If it works, then you at least know that the problem is with your tester and not the connector on the car. You never know, your connector might have been damaged or something and it has nothing to do with your tester. Just a little trouble shooting technique.