exceed: can't open display - Xwindows

i'm connecting to a sun solaris machine via putty, which has /usr/
openwin/bin/xterm

i am testing with 2 windows xp machines on the LAN with Windows XP Pro
SP2, both with Hummingbird Exceed 11 installed. Opening Exceed
application on both machines, I connect with Putty to the solaris
machine:

export DISPLAY={ip address of first machine}:0.0
xterm &

-> the xterm window pops up on machine 1

export DISPLAY={ip address of second machine}:0.0
xterm &

-> nothing happens. after several minutes get the message in putty
terminal: xterm Xt error: Can't open display: {ip address of second
machine}:0.0"

AFAIK, the settings of the two machines are basically the same. how
should i go about resolving this issue?

thx.