window managers don't work over ssh

[Xian]

I cant seem to make any window manager work over ssh, but they all work 
locally. I am using Xorg now, and i didn't have this problem with XFree86.

I start X with just xterm for testing:

 startx /usr/X11R6/bin/xterm

and then type

 ssh -CXf my.home.machine twm

in the xterm and it tells me it cant find any unmanaged screens.

Ive no idea whats doing wrong because other X apps work over ssh and window 
managers work locally.

Any help much appreciated.
-- 
/Xian

"Knowledge speaks but wisdom listens"
Jimi Hendrix