Do "xhost + localhost" before you "su".
Till
Riccardo Ferraro wrote:
> If, as normal user I type "su" then root password and
> try xsane or xscanimage I get:
>
> Xlib:connection to ":0.0" refused by server
> Xlib: invalid MIT-MAGIC-COOKIE-1 key
> Gtk-WARNING ** cannot open display :: 0.0
>