Fortigate HA reverts back to standalone

When you confiugre HA Cluster with Fortigate it reverts backto standalone mode but accepts the other changes like heartbeats,groupname etc…
Then I realised that the all network interfaces must be configured to manual. If you have any DHCP or PPPOE configuration on your interfaces Fortigate doesnt accept HA modes and reverts back to Standalone mode.There is no error message or warning..