The computers are within the same network using WLAN.
The error doesn't always show. Sometimes I can connect without a fuss, and sometimes the error shows.
The Destination Host Unreachable from the PING, means that the ping fails (packet drop).
It would probably be one of
WLAN is more unreliable than wired networks. It can drop packets without dropping the connection. Try to change which channel your network is running on.
To check if it's dropping packets you can have ping running in a window.