VNC cannot connect to vms with Xen 4.3.1 on Fedora 20

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VNC cannot connect to vms with Xen 4.3.1 on Fedora 20 I downloaded Xen 4.3.1 from http://koji.fedoraproject.org/koji/buildinfo?buildID=477343.

I have set vnc-listen and vncpasswd in /etc/xen/xend-config.sxp:

# The interface for VNC servers to listen on. Defaults
# to 127.0.0.1  To restore old 'listen everywhere' behaviour
# set this to 0.0.0.0
(vnc-listen '0.0.0.0')

# The default password for VNC console on HVM domain.
# Empty string is no authentication.
(vncpasswd '')

and set vfb = [ 'vnc=1, vnclisten=0.0.0.0 ,vncunused=1'] in cfg file.

After xm create the vm, xl list shows the vm is started:

[root@localhost qemu-xen]# xl list
Name                                        ID   Mem VCPUs      State   Time(s)
Domain-0                                     0  3298     4     r-----     131.5
2008R2-standard-1                            6   515     2     -b----      21.2

[root@localhost 2008]# ifconfig
em1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 10.74.169.145  netmask 255.255.254.0  broadcast 0.0.0.0

But when I try to connect the vm through vnc:10.74.169.145:6, it returns failed!

What should I do for this problem? I Googled, but nothing obtained...