X11 Forwarding Works On One Host, "Can't Open Display" On Other [PUTTY/XMING]

Question

I have two identical servers, server A and server B. If I connect to server A in Putty and enable X11 forwarding in the settings (running XMING on my PC), everything works fine. I can run all the test commands like 'xeyes' or 'xclock' and they work fine too.

However doing the exact same thing on server B results in a

Error: Can't open display: localhost:10.0

doing

echo $DISPLAY

on both servers returns the same (localhost:10.0) and both servers are on the same network so the firewall rules are identical (though I'm not sure this is relevant as the commands should go through SSH)

What should I try next to get X11 working on server B?

Solution

Got it to work in the end. In /etc/hosts there were the lines

1.2.3.4   server.lan
127.0.0.1 localhost

Reversing those lines so the localhost line was first stopped the errors

Comments

[Toby Mao]

X11Forwarding is enabled in sshd_config, X11 has worked on this server before but it was a while ago I think