If you used GCD or library that depends on it (e.g. Reachability), you should know dispatch_release is no longer needed in iOS 6 with ARC. In fact, if you try to use it, it is a compiler error, just like what happen when you call release in earlier SDK.
To fix it, you may want to remove the dispatch_release, or use preprocessor:
/* header */ #if __IPHONE_OS_VERSION_MIN_REQUIRED >= 60000 #define NEEDS_DISPATCH_RETAIN_RELEASE 0 #else // iOS 5.X or earlier #define NEEDS_DISPATCH_RETAIN_RELEASE 1 #endif /* implementation */ #if NEEDS_DISPATCH_RETAIN_RELEASE dispatch_release(self.reachabilitySerialQueue); #endif