I received the msg
"ERROR {org.apache.axis2.clustering.management.DefaultGroupManagementAgent} - Could not add application member Host .."
in ELB log when updating esb from 4.6.0 to 4.7.0 (I have 2 ESB workers, 1 ESB management, 1 ELB: all worked fine in ESB 4.6.0)
Usually you get this error when ELB detects that at least one port of member is not reachable.
Please check telnet'ing all the ports you have specified in ESB and also the port.mapping (http://nirmalfdo.blogspot.com/2013/09/why-i-need-portmapping-property-when.html) properties specified in axis2.xml file of ESB.
Also you could enable debug logs for "org.apache.axis2.clustering" and get to know the exact issue (as in which port/s is/are not reachable etc.).