ESXi 4.1 Host Won't Join Cluster

We have 3 ESXi 4.1 hosts in a cluster. (It is due to be upgraded, however it is a validated system, and runs qualified VMs, so we can't just upgrade it to the latest edition without a full project & re-validation).
We moved all the VMs off of 1 host, and rebooted the server (needed to check if there was a memory issue). After it was rebooted it appears that it won't connect to the cluster again. If we try to re-add the host, we get an error message:

Call "Datacenter.QueryConnectionInfo" for object "CLUSTER1" on vCenter Server "vCentre.domain.net" failed.

We've tried rebooting again, also checked the VMWare vCenter Agent service is running. But that hasn't helped. I've checked the vpxd.log it seems authd is failing.
I've tried adding

security.host.ruissl = "TRUE"

to /etc/vmware/config file as per VM KB2037351

 Not sure what to try next :

[2016-10-12 16:12:56.975 04720 info 'App' opID=B57F0F0C-000000D3] [VpxLRO] -- BEGIN task-internal-1698 --  -- vmodl.query.PropertyCollector.cancelWaitForUpdates -- A576837F-4FED-4164-ADFB-B2A3CE7D2574(48CCDE4A-41A4-4721-B330-B6043FDBE81A)
[2016-10-12 16:12:56.975 04720 verbose 'App' opID=B57F0F0C-000000D3] [VpxVmomi] Invoke error: vmodl.query.PropertyCollector.waitForUpdates session: A576837F-4FED-4164-ADFB-B2A3CE7D2574 Throw: vmodl.fault.RequestCanceled
[2016-10-12 16:12:56.976 04720 verbose 'SoapAdapter.HTTPService' opID=B57F0F0C-000000D3] User agent is 'VMware VI Client/4.0.0'
[2016-10-12 16:12:56.976 04720 verbose 'SoapAdapter.HTTPService' opID=B57F0F0C-000000D3] HTTP Response: Client: NeedsContentLength: false UnderstandsChunking: true CanKeepAlive: true (PresetContentLength -1)
[2016-10-12 16:12:56.976 04720 verbose 'SoapAdapter.HTTPService' opID=B57F0F0C-000000D3] HTTP Response: Complete (processed 570 bytes)
[2016-10-12 16:12:56.977 04720 error 'App' opID=B57F0F0C-000000D3] Connection lost while waiting for the next request on stream TCPStreamWin32(socket=TCP(fd=2420) local=[::1]:8085,  peer=[::1]:52681): class Vmacore::SystemException(An established connection was aborted by the software in your host machine. )
[2016-10-12 16:12:56.977 04720 verbose 'App' opID=B57F0F0C-000000D3] [VpxVmomi] Invoke done: vmodl.query.PropertyCollector.cancelWaitForUpdates session: A576837F-4FED-4164-ADFB-B2A3CE7D2574
[2016-10-12 16:12:56.977 04720 verbose 'SoapAdapter.HTTPService' opID=B57F0F0C-000000D3] HTTP Response: Complete (processed 414 bytes)
[2016-10-12 16:12:56.978 04720 info 'App' opID=B57F0F0C-000000D3] [VpxLRO] -- FINISH task-internal-1698 --  -- vmodl.query.PropertyCollector.cancelWaitForUpdates -- A576837F-4FED-4164-ADFB-B2A3CE7D2574(48CCDE4A-41A4-4721-B330-B6043FDBE81A)
[2016-10-12 16:12:57.209 04720 verbose 'ProxySvc Req00861'] New client SSL(TCPStreamWin32(socket=TCP(fd=2132) local=10.20.2.78:443,  peer=10.32.30.54:54078))
[2016-10-12 16:12:57.326 04720 verbose 'SoapAdapter.HTTPService'] User agent is 'VMware VI Client/4.0.0'
[2016-10-12 16:12:57.326 04720 verbose 'SoapAdapter.HTTPService'] HTTP Response: Client: NeedsContentLength: false UnderstandsChunking: true CanKeepAlive: true (PresetContentLength -1)
[2016-10-12 16:12:57.327 04720 verbose 'App'] [VpxVmomi] Invoking [waitForUpdates] on [vmodl.query.PropertyCollector:session[A576837F-4FED-4164-ADFB-B2A3CE7D2574]6ECC220B-329A-4CE0-8409-5206AE198E4C] session [A576837F-4FED-4164-ADFB-B2A3CE7D2574(48CCDE4A-41A4-4721-B330-B6043FDBE81A)]
[2016-10-12 16:12:57.722 03948 info 'Libs' opID=500C55A7-000001BB] Cannot connect to server esxhost2:902: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond
[2016-10-12 16:12:57.722 03948 info 'Libs' opID=500C55A7-000001BB] CnxAuthdConnect: Returning false because CnxAuthdConnectTCP failed
[2016-10-12 16:12:57.722 03948 info 'Libs' opID=500C55A7-000001BB] CnxConnectAuthd: Returning false because CnxAuthdConnect failed
[2016-10-12 16:12:57.722 03948 info 'Libs' opID=500C55A7-000001BB] Cnx_Connect: Returning false because CnxConnectAuthd failed
[2016-10-12 16:12:57.722 03948 info 'Libs' opID=500C55A7-000001BB] Cnx_Connect: Error message: Failed to connect to server esxhost2:902
[2016-10-12 16:12:57.722 03948 error 'App' opID=500C55A7-000001BB] [VpxVmdbCnx] Authd error: Failed to connect to server esxhost2:902
[2016-10-12 16:12:57.722 03948 error 'App' opID=500C55A7-000001BB] [VpxVmdbCnx] Failed to connect to host esxhost2:902. Check that authd is running correctly (lib/connect error 2)
[2016-10-12 16:12:57.722 03948 verbose 'App' opID=500C55A7-000001BB] [VpxVmdbCnx] Failed to connect to host <esxhost2>
[2016-10-12 16:12:57.722 03948 verbose 'App' opID=500C55A7-000001BB] [VpxdHostAccess] Disconnecting from esxhost2
[2016-10-12 16:12:57.722 03948 error 'App' opID=500C55A7-000001BB] vim.fault.NoHost