Why is Mathf.Pow( <some float value>, <some value less than 1> ) returning NaN on iOS 4.2 beta?

If this problem only occurs on this beta OS, it's likely because it's a beta. Is it only this line that presents the problem or does it happen elsewhere? You're sure levelNumber is being assigned? You could always write your own Pow function. If you just want to do a root (yth root of x = x^(1.0/y)), you could just write a root function with Newton's Method or something, hardcoding whatever you can.

If the Pow function is working correctly then I think that your Pow function will return NaN only when the first argument < 0 So, you should check and make sure that levelNumber is properly assigned. You may want to check if your variable is properly initialized too.

@slovacs1 there's another line of code that does a similar cube root calculation that also returns NaN for the pow. I'm sure my variable is being initialized; on pre-4.2 versions of the OS the math works as expected.

I tested Pow through all relevant combinations, and as loginjjobby suggested, Pow returns NaN when the base is negative, but specifically only when the base is negative AND the exponent is a fraction. Since you are certain that levelNumber is positive and it only seems to happen on this beta OS, I would still look to the OS as the source. At this point, if you are 100% certain that levelNumber is positive, I can only suggest checking with Apple or writing your own cube root function (if you are only doing cube roots).