Compile error trying to use CAGradientLayer

I'm trying to use CAGradientLayer and getting an unhelpful compile error. Can't figure out whats wrong. All I'm doing so far is:

CAGradientLayer *gradient = [CAGradientLayer layer];

I've imported <QuartzCore/QuartzCore.h> and I'm getting the warning >

_OBJC_CLASS_$CAGradientLayer referenced from: objc-class-ref-to-CAGradientLayer symbol(s) not found.

I've tried clean and build but no luck and I can't seem to target anything other than 4.1 in Xcode

Cheers for any help.