I'm trying to set up a ssh server on my computer and it's giving me an error when I try to ssh into it:

[COMMENT]root@bt:~# ssh localhost
root@localhost's password:

BackTrack 4 (PwnSauce) Penetration Testing and Auditing Distribution

Last login: Mon Jul 12 02:50:25 2010 from localhost

X: warning; process set to priority -1 instead of requested priority 0

Fatal server error:
Server is already active for display 0
If this server is no longer running, remove /tmp/.X0-lock
and start again.
[/COMMENT]

As you can see, I'm not even running it with the '-X' option, but it's still giving me that error. What's the cause of this and how can I fix it?