ESXI corrupted after attempted roll back from 6.0 to 5.0

[BillAdams]

I had to roll back to ESXi 5.5 after upgrading to 6.0

The install still appears to be 6.0.

It says 6.0 on the  DCUI screen.

I can connect to this host with Vsphere 6.0 but not Vsphere 5.5.

Is there a fix?

I'm thinking I need to format and start over. How do I format without losing the VMs that are on it?

Not a VMWare expert.

Thanks in advance. 

[e_espinel]

Hello.
The first thing is to verify that your hardware supports version 6.0, if your server is branded it is easier to verify this in the following link, otherwise you will have to check for its internal parts, such as CPU, internal disk controller, ethernet card and any other important internal device.

http://partnerweb.vmware.com/comp_guide2/search.php

If your server is a branded server such as HP, Lenovo, Dell and more, it is best to obtain and install VMware with a custom image from the server manufacturer.

Another issue to consider is that version 6 requires a 6 license.

You should consider making a Full backup (complete copy) of your data (VMs).

The simplest method is:
1. shutdown all VMs in normal way.
2. boot the server with the CD/DVD with the VMware vSphere image.
3. Choose the option to install ESXi and preserve the VMFS Datastores
4. reconfigure the ESXi host (name, IP, Gateway, DNs and so on).
5. Include the VMs in the VM inventory on the ESXi host and root them.