xterm Xt error: Can't open display: %s 은 어떻게 하나요?

윈7 xmanager에서 원격 centos5.5에 접속할 때 이 오류 메세지가 나옵니다.

/usr/bin/xterm Xt error: Can't open display: %s

원격 centos의 설정은 다음과 같이 했습니다.

[xdmcp]
Enable=true

Firewall (TCP/UDP Ports) Configuration
Open UDP port 177 from the PC to the remote host direction.
Open incoming TCP ports 6000~6010 from the remote host to your PC.
After adding these ports "/etc/sysconfig/iptable" as the enoder mentioned, /etc/init.d/iptables restart
# Xmanager
-A RH-Firewall-1-INPUT -p tcp -m tcp --dport 6000:6100 --syn -j ACCEPT
-A RH-Firewall-1-INPUT -p tcp -m tcp --dport 7100 --syn -j ACCEPT
-A RH-Firewall-1-INPUT -p udp -m udp --dport 177 -j ACCEPT

/ssh/sshd_config

X11Forwarding yes

iptables -L 의 결과는 이렇습니다.

Chain INPUT (policy DROP)
target prot opt source destination
RH-Firewall-1-INPUT all -- anywhere anywhere

Chain FORWARD (policy DROP)
target prot opt source destination
RH-Firewall-1-INPUT all -- anywhere anywhere

Chain OUTPUT (policy ACCEPT)
target prot opt source destination

Chain RH-Firewall-1-INPUT (2 references)
target prot opt source destination
ACCEPT tcp -- anywhere anywhere tcp dpt:domain
ACCEPT udp -- anywhere anywhere udp dpt:domain
ACCEPT all -- anywhere anywhere state RELATED,ESTAB
LISHED
ACCEPT tcp -- ipc.server.com anywhere state NEW tcp dp
t:ftp
ACCEPT tcp -- xxx.xxx.xx.xxx anywhere state NEW tcp dpt:f
tp
ACCEPT tcp -- ipc.server.com anywhere state NEW tcp dp
t:ssh
ACCEPT tcp -- xxx.xxx.xx.xxx anywhere state NEW tcp dpt:s
sh
ACCEPT tcp -- anywhere anywhere state NEW tcp dpt:h
ttp
REJECT all -- anywhere anywhere reject-with icmp-ho
st-prohibited
ACCEPT tcp -- anywhere anywhere tcp dpts:x11:synchr
onet-db flags:FIN,SYN,RST,ACK/SYN
ACCEPT tcp -- anywhere anywhere tcp dpt:xfs flags:F
IN,SYN,RST,ACK/SYN
ACCEPT udp -- anywhere anywhere udp dpt:xdmcp

원격서버의 방화벽을 정지할 형편이 안되니 일이 어렵습니다.

해결할 방법이 없을까요?