Ever been in the situation where you log on to a server as one user having X11 enabled, but then need to sudo to another one – and voila, your X11-sesison is long gone…
Solution provided here http://brandonhutchinson.com/wiki/X11_Forwarding_and_su/sudo
I did as root
cd ~
mv .Xauthority .Xauthority_old
ln -s ~diagnostics/.Xauthorithy .Xautorithy
and it all worked fine.