yup I got that too for some and had that problem when kid and I were trying to add eachother. he's on it now but it happened with others. sometimes after I logged and came back it would work it'self out and other times I think I had to just wait again for both a friend and I to be on and add them.
I dont know but it's buggy.
on unrelated note : the top lists are all messed up I notice. if you click the show my rank and friends (whatever it's called) it shows me names I don't recognize and pretty sure aren't even on my friendlist and also slots where it says 'deleted' and totally looks like there is a problem with the top list pages.
other issues mentioned in other posts are no friends numbers showing up on website front page, no friends numbers listed on log in screens for game.
my guess is all the buggy stuff is all connected to the flist update and needs some kind of looksie over.
Slow but steady wins the race or something like that.
I'm just taking it slow, not sure about the steady.
*Pre-Steam release Player*
*Joined Spring of 2014 *