Xlib: connection to ":0.0" refused by server Xlib: No protoc…

Xlib: connection to ":0.0" refused by server
Xlib: No protocol specified

^^^^^^^^^^^
error message if I try to run bluefish ...

root@server: #su craig -c bluefish &

if I exit su and run it as craig@server: # it works

I continue to have problems running commands as root with the su command
as above. man su and info su just don't get the point across to me. Can
anyone point me to a page that describes GNU su ?

Thanks,

Craig