I have a Linux Mint 13 Xfce in a VMware Workstation 8 VM and set the resolution from 800x600 to 1280x768 and now I get permanently logged out when I try to login.
I knew how to get back to my old resolution back in the xorg.conf days but Linux Mint now uses xrandr which won't display any displays when running # xrandr because X is not running (of course not - I can't login over GUI).

I know that there are configuration files in /etc/X11/Xsession.d/ because I configured a debian based thinclient's resolution in a file called /etc/X11/Xsession.d/91configure_display but that file doesn't exist in my Linux Mint VM.

So, how do I reset my X screen resolution from console?

Edit: I forgot to tell you that I can't change resolution in console:

# xrandr -s 800x600
Can't open display

This message appears every time I use xrandr or xrandr -s *resolution*

Update:
I tried what bWowk suggested:

# export DISPLAY=:0.0
# xrandr -s 800x600
No protocol specified
No protocol specified
Can't open display :0.0

So, that doesn't work either. Isn't there a configuration file that is executed every time X starts?
X is running btw - ps aux | grep X shows one process /usr/bin/X running.