Looking at the source code here and here it looks that both
- (id)objectWithString:(NSString*)jsonText error:(NSError**)error
and
- (id)JSONValue;
are deprecated since version 3.2 and it will be removed in version 4.0. Are you sure you are using the 3.1?
On the other hand both
- (id)objectWithString:(NSString *)repr;
and
- (id)objectWithData:(NSData*)data;
look available and not deprecated.
I would suggest you to use them instead.
An alternative is to use the NSJSONSerialization class provided by Apple.