Assuming you can disconnect from the internet the router that these computers are connected to, disable the firewalls on both machines.
1) login as root in the command prompt
2) disable the firewall
whatever the firewall is in debian stop it.
Now try the SSH for both of these machines. If that can work you can say that it is a firewall issue.
Process of elimination:
physical, both are connected to the AP
data link and networking, ping and internet work
transport, ports may not be opened to receive data (firewalla issue)