Error 10060 is a time-out error. It can be caused by a bad or improperly configured router or firewall. 10060 - Connection Timed Out - caused by mismatched port numbers, invalid IP address, or Server not turned on, among other things.
This error is caused by the Endpoint being unable to contact the Server for some reason.
If this happens with just one client, and the rest are OK, and this client has been running OK in the past, find out what changed on the Client end and revert. It might have been a windows update, a new antivirus or update, a reinstallation of the Client software, a new firewall or new routing rules on the Client side, or anything else that stops the client from communicating over the Internet with its RBS Server.