Xlib: connection to ":0.0" refused by server

[João Salvatti]

Hi all,

I've installed NVU (from ports). Everything worked fine while installing it, but
when I run the program it displayed the following message:

 Xlib: connection to ":0.0" refused by server
 Xlib: XDM authorization key matches an existing client!

 (nvu-bin:45268): Gtk-WARNING **: cannot open display:

I've started the program by the console logged as a ordinary user. It also
happens when I try to run Firefox:

  Xlib: connection to ":0.0" refused by server
 Xlib: XDM authorization key matches an existing client!

 (firefox-bin:45297): Gtk-WARNING **: cannot open display:

How can I solve this problem?

Thanks for now!
-- 
João Salvatti