Well, i dont soley use oranges and tanges's I use zucc, apples, romaine, pears, strawberry, melon, carrots, etc... I think using too much of any one item is the prob. As long as your using variety you should be fine. I should have stated that earlier.
I know the oranges are good cause the breeder where I got my cham uses them in her gutload and they have been breeding gorgeous healthy chameleons for many many years. Don't know how they compare to a tangerine though.