an unknown error occured (4013) this is the only thing that i can see during the restore of my iphone... !!

my iphone was working on 5.1 and i updated it to the latest.. after updating.. my phone is just showing a sign. to connect it to the itunes..
however i connected it to the itunes.. and there was an option of [restore and update] so i did since then it is showing again and again an unknown error occured (4013). now what should i do..?? i even updated my itunes to the latest.. !! :/