openstack multi-node failue with devstack

I followed http://devstack.org/guides/multinode-lab.html to get my multi-node openstack envoriment installed(One master node with hostname "Andy",and one compute node with hostname "ubuntu-185").I hava checked the database that ubntu-185 was in table compute_nodes,and table services has compute and network service of ubuntu-185.but when it try to deploy VM to ubuntu-185,it get error as follow:

Previously tried hosts: []. (host=ubuntu-185)
2012-11-04 15:58:28,330 host 'ubuntu-185': free_ram_mb:1466 free_disk_mb:93184 is disabled or has not been heard from in a while
2012-11-04 15:58:28,331 Host filter function <bound method ComputeFilter.host_passes of <nova.scheduler.filters.compute_filter.ComputeFilter object at 0xa18e16c>> failed for ubuntu-185

Andyone can help me solve this problem,I'll be more than appreciated!