X->XX->X problem

[vp@example.com (Viktor Pavlenko)]

I just showed a colleague how great linux is by starting a second
X server (with startx -- :1); it came out at F9 for some reason;
if I pressed F8 the screen would blink and switch to F7 again.

Anyway, I killed the second X, and now strange things start happening
with the first one:

$ xterm&
[2] 5226
Xlib: connection to ":0.0" refused by server
Xlib: Invalid MIT-MAGIC-COOKIE-1 key
xterm Xt error: Can't open display: :0
[2]+  Exit 1                  xterm

$ xhost +
Xlib: connection to ":0.0" refused by server
Xlib: Invalid MIT-MAGIC-COOKIE-1 key
xhost:  unable to open display ":0"

Anything I can try brefore restarting X?

(this may be relevant: I have Matrox card (chipset mgag400),
driver mga_hal_drv.o and run X on double screen)

Thanks
Viktor