Zero, its because your steam has updated but the servers have not, only a matter of time before you can join! or at least i think its that because i have the same issue!
I say chaps, these dastardly non-steamers cannot connect! Tea and biscuits for everyone, huzzah! In all seriousness, I think Example hit the nail on the head
we didnt think we knew we hacked ur pc and added some tentical porn on it and see if u would watch it... which u did :l