Cannot give access to X-Server to other users on same machine

["Francisco M. Marzoa Alonso" <fmmarzoa@gmx.net>]

The trouble:

fmmarzoa@crom:~$ xhost +localhost
localhost being added to access control list
fmmarzoa@crom:~$ su -
Password: 
crom:~# export DISPLAY=":0.0"
crom:~# kreatecd
Xlib: connection to ":0.0" refused by server
Xlib: Client is not authorized to connect to Server
kreatecd: cannot connect to X server :0.0
crom:~#

¿The solution?

TIA