wrong authentication protocol attempted

From: Jack Patteeuw (jjpatteeuw_at_nospam.net)
Date: 10/27/05 

Date: Thu, 27 Oct 2005 00:36:22 GMT

PuTTY 0.56

I'm using PuTTY to tunnel X11 which works just fine.

When I su I want to forward X11 so I do the following

        user> xauth extract /tmp/MIT-MAGIC-COOKIE $DISPLAY
        su -
        Password:
        root> xauth merge /tmp/MIT-MAGIC-COOKIE
        root> DISPLAY=`hostname`:10.0
        root> export DISPLAY
        root> xclock
        Xlib: connection to "<myhost>:10.0" refused by server
        Xlib: PuTTY X11 proxy: wrong authentication protocol attempted
        Error: Can't open display: <myhost>:10.0

I have Remote X11 authentication protocol set to MIT-Magic-Cookie-1 in PuTTY

What is really odd is this DOES work correctly on a diferent host which
(in theory) has been set up the same !!????