GTM: Virtual Server are offline

Hi Experts,

I have configured a server in F5 DNS(GTM). Inside the server I have configured a virtual server. But GTM shows server offline.

I set 10.10.80.x:80 as the server( This is VIP configured in a Cisco ACE Load Balancer).I also set 10.10.80.x:80 as the virtual server.

The service is up an running at 10.10.80.x:80, but still GTM marks it as offline.

I attached gateway_icmp monitor to Server and /common/http inside the virutal server.

gtm server Test {
    addresses {
        10.10.80.x {
            device-name Test
        }
    }
    datacenter xxx
    monitor gateway_icmp 
    product generic-host
    virtual-servers {
        Test {
            destination 10.10.80.x:http
            monitor http 
        }
    }
}

(LTM-01)(cfg-sync Standalone)(Active)(/Common)(tmos) show gtm server Test

-------------------------------
Gtm::Server: Test (Unit: 0)
-------------------------------
Status                
  Availability : offline
  State        : enabled
  Reason       : No enabled VS available

Global                
  Virtual Server Picks   0
  Connections            0

Throughput              In  Out
  Bits/sec               0    0
  Packets/sec            0    0

(LTM-01)(cfg-sync Standalone)(Active)(/Common)(tmos) telnet 10.10.80.x 80
Trying 10.10.80.x...
Connected to 10.10.80.x.
Escape character is '^]'.

I am wondering why this config is NOT working. Any help would be appreciated.