A Customer Has Two Cisco 550B WLCs That Manage All

A customer has two Cisco 550B WLCs that manage all the access points in their network and provide N+1 redundancy and load balancing. The primary Cisco WLC has 60 licenses and the secondary Cisco WLC has 40. The customer wants to convert the N+1 model to an HA model and provide SSO. Configuration must be performed during a maintenance window. After performing all the configurations on both controllers, the config redundancy unit secondary command is issued on the secondary Cisco WLC and it fails. Which parameter needs to be in place to complete the configuration?

A) A cable in the RP port
B) The secondary Cisco WLC needs a minimum of 50 base licenses
C) The primary Cisco WLC is already set as the secondary unit.
D) SSO needs to be enabled