NSData+Base64.h XCode 4.5 iOS 6

If you are getting following error:

'NSInvalidArgumentException', reason: 
'-[NSConcreteData dataUsingEncoding:]: unrecognized selector sent to instance

while using NSData+Base64 category, make sure that object you are passing to

+ (NSData *)dataFromBase64String:(NSString *)aString

is actually of type NSString *.