itunes won't connect to new iphone 6 s plus

When I connect my new Iphone 6s plus it give me the message to update my itunes to a newer version- - I have both the latest version of itunes 11.4 on my macbook pro- and have just completed the latest iphone update- ios 9.3.1- - - still getting the same error- - - what do i do? this is very frustrating.