After shooting Lord of the Rings, Gollum apparently had some time over and worked at Apple writing error messages for some of the odder errors.
It's a typo. There are worse typos in the OS, particularly if you check the translations. The problem is that spell checking messages like this is tricky - it's most likely hardcoded in a C-file. If you're high enough up that you're in Interface Builder, I think that there is a spellchecker for it these days, but there is no spellchecker in vi.