Cannot connect to FW via ha-mgmt-interface

I formed a cluster with 2 Fortigate 200B firewall and could like to management them separately by different IPs. However, I cannot ping any one of them even through I enable the Reserve Management Port for Cluster Member. 

The firmware version is 5.2.10

Below are one of the member configuration

HA configuration:

set ha-mgmt-status enable set ha-mgmt-interface "port10" set ha-mgmt-interface-gateway 172.xx.xx.254

System interface configuration:

edit "port10" set ip 172.xx.xx.224 255.255.255.0 set allowaccess ping https http set vlanforward enable set type physical set snmp-index 12

The above configuration should be fine. Anyone had the same question before?

Any help would be appreciated. Thanks.