I think there's three possible answers: 1. The person needs some salt (maybe they are cooking something that requires salt) and they have no salt. 2. Someone actually said "I'm out of sorts." and someone else has misheard the sentence. 'I'm out of sorts' is an idiom that means 'I feel slightly unwell.' (either physically or mentally/emotionally) 3. Thousands of people have misheard the idiom 'out of sorts' and gradually all these people keep repeating "I'm out of salt." in the belief that this is the correct idiom... and perhaps gradually it will become an accepted version of the original idiom... but for now it would be considered non standard