X11 Forwarding can't open display (client rejected?)

In Putty, I’ve enabled x11 forwarding, with the ‘X display location’ set to 0.0

The BBB’s X -version is 1.16.4, with the the /etc/ssh/ssh_config set to:

ForwardX11 yes
ForwardX11 Trusted yes

and /etc/ssh/sshd_config:
X11Forwarding yes

I’ve also forced the DISPLAY variable to point to my local machine’s IP:
export DISPLAY=192.168.1.140:0.0
and verified it’s set correctly (using ‘echo $DISPLAY’)

Finally restarted, ‘service ssh restart’ and ‘service sshd restart’

Unfortunately, when I enter ‘xterm&’, I get the error
“Can’t open display: %s”

and the locally running xming (Win8) never shows anything. Interestingly, the Xming log seems to show an authentication error?

winClipboardProc - Hello
DetectUnicodeSupport - Windows Vista
winClipboardProc - DISPLAY=127.0.0.1:0.0
winMultiWindowXMsgProc - XOpenDisplay () returned and successfully opened the display.
winInitMultiWindowWM - XOpenDisplay () returned and successfully opened the display.
winClipboardProc - XOpenDisplay () returned and successfully opened the display.
AUDIT: Mon Jul 04 09:40:48 2016: 2508 C:\Program Files (x86)\Xming\Xming.exe: client 4 rejected from IP 192.168.1.151
[Note: the 192.168.1.151 is the IP of the BBB (ifconfig -a)]

Any ideas what could be the problem? Anyone else try this on the beaglebone black (Debian 8.4)?