Why does it often say "That player is currently busy" when trying to trade in hideout?

I invite player, they arrive in my hideout. I try to open trade and it says "That player is currently busy". We stand there staring at each other for a few seconds and then they piss off :D

Update - I read somewhere that the visiting player needs to move around a little off of the waystone. The next player I invited did this after failing first time and then it worked ok. Huh.