为什么我在试图释放的时候得到了EXC_BAD_的访问权限?

请看一下我的代码:

(void)loadContactsFromAddressBook {
ABAddressBookRef addressBook = ABAddressBookCreate();
CFArrayRef allPeople = ABAddressBookCopyArrayOfAllPeople(addressBook);
CFIndex count = ABAddressBookGetPersonCount(addressBook);
ABRecordRef person;

for (int i = 0; i < count; i++) {
    person = CFArrayGetValueAtIndex(allPeople, i);
    CFStringRef cfStr = ABRecordCopyValue(person, kABPersonFirstNameProperty);
    NSString* firstName = (NSString*) cfStr;
    [contacts addObject:firstName]; 
    CFRelease(cfStr);
}

CFRelease(addressBook);
CFRelease(allPeople);
}

我试图在for块后CFRelease(person),但应用程序因EXC_BAD_ACCESS而崩溃。如果我删除CFRelease(person),则应用程序工作。