openssh unix dev - Mar 2000 - X11Forwarding problem

I have just installed openssh-1.2.2p1-1
on two of my machines and I have one problem.

I have 
X11Forwarding yes
in my /etc/ssh/sshd_config

but when I try to ssh to that machine I get this when i try to start rxvt:

[pucko at b202 pucko]$ rxvt
X11 connection rejected because of wrong authentication.

X connection to b202.ryd.student.liu.se:11.0 broken (explicit kill or
server shutdown).   [pucko at b202 pucko]$

The strange thing is that it works if I do the same thing as root.

What can be wrong?

/M