I can't use either Empathy or Pidgin to reply to some users using the "people nearby" / people near me / bonjour / avahi protocol. I can receive messages from them, it will arrive on my machine, but when I send a reply I receive an error sending message "[message]": disconnected error. If they send me more messages I get those as well.
This happens only to some users on the local network, with other local users I can chat just fine.
Error on Empathy:
The same issue on Pidgin: