Discharge from the Army during WWI

Doing some family tree stuff, and found this statement on an army discharge book.

"Not likely to become an efficient soldier Para 392 KR".

Has anybody got any idea what this means specificaly? I assume that KR is Kings Regs, But what's Para 29??

I mean it looks pretty bad that your country doesn't want you, when the were send men and boy to the slaughter en mass

Funny though, coincidentaly the chap concerned had a cousin who got dropped for joining up under age and another that got killed.