解决办法:

Had the same issue, I was trying to set the output straight to a dictionary I had created.
myDictionary = [string objectFromJSONString];

solved it by setting the output to a temporary dictionary and making a copy
NSDictionary *tempDictionary =[string objectFromJSONString];
myDictionary = [tempDictionary copy];

JSONKit is a very nice tool I will continue to use it!