Archiving / Unarchiving results in initForReadingWithData incomprehensible archive

I've implemented an save on `applicationWillTerminate` and load on `applicationWillFinishLoading`. There is a complete object tree, all implement the `NSCoding` protocol and I've check the types I enter. One of the classes also stores an `NSMutableData` to the `NSKeyedArchive`, which I suspect might break unarchiving occasionally. Weirdly enough, sometimes it works and sometimes it doesn't. I suspect some content in the `NSMutableData` will break the archiving. I use encodeObject on all objects, except for the bools and int where I use the correct corresponding method (`encodeBool:forKey:` and `encodeInt:forKey:`) To be more clear: the code really does work, sometimes is it able to rebuild a rather complete object graph, just not all the time. The error message I get is: ``` initForReadingWithData incomprehensible archive 0x62, 0x70, 0x6c, 0x69, 0x73, 0x74, 0x30, 0x30 ``` Added: code which is failing, it an `NSMutableData` of 10+ MB ``` - (void)encodeWithCoder:(NSCoder*)encoder { [encoder encodeObject:self.encodedMessage forKey:@"EncodedMessage"]; //NSData [encoder encodeObject:self.data forKey:@"Data"]; //NSMutableData (10+MB) [encoder encodeObject:self.header forKey:@"Header"]; //NSString [encoder encodeObject:self.fileName forKey:@"FileName"]; //NSString [encoder encodeInt:self.dataStartIndex forKey:@"DataStartIndex"]; //int [encoder encodeInt:self.dataEndIndex forKey:@"DataEndIndex"]; //int } - (id)initWithCoder:(NSCoder*)decoder { if (self = [super init]) { self.encodedMessage = [decoder decodeObjectForKey:@"EncodedMessage"]; //NSData self.data = [decoder decodeObjectForKey:@"Data"]; //NSMutableData self.header = [decoder decodeObjectForKey:@"Header"]; //NSString self.fileName = [decoder decodeObjectForKey:@"FileName"]; //NSString self.dataStartIndex = [decoder decodeIntForKey:@"DataStartIndex"]; //int self.dataEndIndex = [decoder decodeIntForKey:@"DataEndIndex"]; //int } return self; } ``` When I remove the self.data encoding and decoding it always seem to work. It also fails with smaller sized self.data. Doesn't seem size but content issue? Tried to open the file when I did write the nsmutabledata to it, the propertly list editor displays the error: ``` "Conversion of string failed. The string is empty." ``` plutil also gives this error: ``` "$ plutil -lint nzbvortex.state nzbvortex.state: Conversion of string failed. The string is empty." ```