ERROR: "Unrecognized task serialized by Server; missing Registration?"

Hello, I get the following error "Unrecognized task serialized by Server; missing Registration?" when playing with a guildy on the Texas US server while I log into the CA server (I also logged in to the TX sever with the same issue). When I try to teleport to him, the game crashes (5 times in mins - and yes I tried with two different characters), and a white bow window pops up saying "Unrecognized task serialized by Server; missing Registration?". Both of us play via the Steam Client, and verified the integrity of the game files. We seem to get stuck in the different versions, or phases of the instance, the there's some syncing issues with out location causing the error. This happened the other day as well numerous times a few days ago, but always with the same person, and never with anyone else... very odd, only his account so far.