CCNA, CCNP, MCSA, CCNA Final Exam, All Answer Test Module With 100/100

I'm trying to convert an NSDictionary to NSData to store in core data, but I am getting a nil value returned to me. error states 'Unknown format option' after the call. NSString *error = nil; NSData *d = [NSPropertyListSerialization dataFromPropertyList:data format:NSPropertyListImmutable errorDescription:&error]; The data I'm trying to convert is an NSDictionary with NSStrings as keys and values. Here is a dump of the data dictionary: Printing description of data: <CFBasicHash 0xc96fd60 [0x18ecb38]>{type = immutable dict, count = 4, entries => 0 : <CFString 0x17c9fc [0x18ecb38]>{contents = "title"} = <CFString 0xecc8040 [0x18ecb38]>{contents = "test"} 1 : <CFString 0x17ca2c [0x18ecb38]>{contents = "author"} = <CFString 0xc9643f0 [0x18ecb38]>{contents = "test"} 2 : <CFString 0x17ca0c [0x18ecb38]>{contents = "goal"} = <CFString 0xc96f730 [0x18ecb38]>{contents = "te