I wonder if it's Odin related: a couple of months ago I unbranded my s4 installing an official rom with Odin. Don't know why but since then Kies labels my phone as not updatable (same csc as before). This happens after the 4.4.2 update with Odin too. Does Kies update work for you?
Inviato dal mio GT-I9505 utilizzando Tapatalk