I can't send a private message to a friend

I am using Internet Explorer 11. I am trying to start a conversation with a friend by clicking on the message button in the right upper corner, and then on "New Message". When I type the friend's name under "Recipients", a box opens on the right and says "No matches were found". If I try to type the message content, the recipient's field gets cleared.

If I go to list of my friends under Friends, therre is no option to send a message, only a link "Connect", which allows me to "Email subsribe to a user" and "Unfriend".

When a friend tries to send a message to me by hovering over my name and selecting "Send a private message", he gets a following error:

So, how do I communicate privately with a customer?

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