using more than 8 temperature probe of DS18B20 on Arduino
As far as I can see there is no limit on the number of sensors you can have on a bus.

So if you are having problems does your code work with less sensors? Try one and work up.

Is it a current issue are you pulling to much from the board?

Is the problem with the one wire library? 

Have you got 4.7k pull ups on each sensor?