IN your code you are writting NSData to NSCoder, so you need to read NSData then convert it to Array.
NSURL *appSupportDir = [[NSFileManager defaultManager] URLForDirectory:NSApplicationSupportDirectory inDomain:NSUserDomainMask appropriateForURL:nil create:YES error:&error];
NSString *path = [NSString stringWithFormat:@"%@/DEConvert.dat",[appSupportDir path]];
NSLog(@"%@",appSupportDir);
NSData *data = [NSData dataWithContentsOfFile:path];
NSMutableArray *arr = [NSKeyedUnarchiver unarchiveObjectWithData:data];
to store object in NSUserDefault
NSData *data = [NSKeyedArchiver archivedDataWithRootObject:arr];
[[NSUserDefaults standardUserDefaults] setObject:data forKey:@"your key"];
Unarchiving is just as easy:
NSData *NewData = [[NSUserDefaults standardUserDefaults] objectForKey:@"your key"];
NSArray *arr = [NSKeyedUnarchiver unarchiveObjectWithData:NewData];