The Ubisoft server for Uplay is a real pain in the arse. I had problems with Uplay with the Assassins Creed series of games. The only one that worked with Uplay was Assassins Creed Brotherhood.
So, when I couldn't connect to Uplay to get the SCAR-H or the uniform with the strange name, I loaded up Assassins Creed Brotherhood and connected to Uplay that way. After that it was a oiece of cake to redeem my Uplay points for the SCAR and uniform as well as Infiltration mode.
If you have any of the AC games, load them up and try to connect to Uplay from them. One of them is bound to work.