Unable to reconfigure HA on VMware ESXi 5.5.0 hosts after failed vCenter upgrade

Problem

You’ve recently attempted to upgrade vCenter 5.5 from 3b to 3e but had to rollback the upgrade to a previous snapshot due to an issue.  Since the upgraded vCenter server was briefly started and had upgraded the HA agents on the ESXi hosts, you now see alarms thrown for the cluster as well as the hosts. The following is one of those errors:

Configuration Issues

There was an error unconfiguring the vSphere HA agent on this host. To solve this problem, connect the host to a vCenter Server of version 5.0 or later.

Attempting to use the Reconfigure for vSphere HA feature on the hosts fails and disabling then re-enabling HA on the cluster also fails.

Solution

To resolve this issue, the first step to try is disable HA on the cluster then follow instructions for reinstalling the HA agent as outlined in the following KB:

Verifying and reinstalling the correct version of the VMware vCenter Server agents (1003714)
https://kb.vmware.com/kb/1003714

Since the environment shown above is ESXi 5.5, the following commands were executed:

~ # cd opt/vmware/uninstallers/

/opt/vmware/uninstallers # ls

VMware-fdm-uninstall.sh

/opt/vmware/uninstallers # cp /opt/vmware/uninstallers/VMware-fdm-uninstall.sh /tmp

/opt/vmware/uninstallers # chmod +x /tmp/VMware-fdm-uninstall.sh

/opt/vmware/uninstallers # /tmp/VMware-fdm-uninstall.sh

/opt/vmware/uninstallers #

If completing the above continues to throw the same error, proceed and try to use the following commands to manually remove the FDM VIB:

~ # esxcli software vib list | grep -i fdm

vmware-fdm 5.5.0-3252642 VMware VMwareCertified 2016-06-23

~ # esxcli software vib remove -n vmware-fdm

Removal Result

Message: Operation finished successfully.

Reboot Required: false

VIBs Installed:

VIBs Removed: VMware_bootbank_vmware-fdm_5.5.0-3252642

VIBs Skipped:

~ #

~ # esxcli software vib list | grep -i fdm

~ #

Once completed, restart the host and attempt to re-enable HA on the cluster to configure the hosts.