NSUserDefaults errors in logs

Question

I get some error messages in logs

[User Defaults] Failed to write value for key GameId in CFPrefsPlistSource<0x1740faf00> (Domain: xxx.xxxxxx, User

Answer 1

I was getting a similar error:

[User Defaults] attempt to set  for key in  in read-only (due to a previous failed write) preferences domain CFPrefsPlistSource<0x1700f5f80>

but it only happened when I was plugged into Xcode.

A device reboot fixed this.