When compiling with the latest Xcode 5 preview 3 I got the following errors:
XYPieChart.m:444:22: Implicit conversion of C pointer type 'CGPathRef' (aka 'const struct CGPath *') to Objective-C pointer type 'NSString *' requires a bridged cast
XYPieChart.m:444:22: Incompatible pointer types sending 'CGPathRef' (aka 'const struct CGPath *') to parameter of type 'NSString *'

This seems to fix it