In Star Wars Episode V: The Empire Strikes Back, when they get back to the Millennium Falcon after escaping from Hoth, C-3PO calls Han "Captain Turner" twice during the panic when they escape into an asteroid field.
Why does he use this name?
I believe this is in Episode V, "Empire Strikes Back," and if so I remember the instances you are talking about (watched "ESB" way too much...or not enough). I've always thought it was just his English accent. The original "Star Wars" trilogy is full of rushed and unclear dialogue (I thought Han Solo was saying "Boat attack" instead of "Boba Fett" in "ROTJ" for years) and dual pronunciations (Leia/Lee-a).