I was recently configuring Lockdown Mode in my lab environment when I discovered an issue where I could not configure the status on a single ESXi host system where the state was Disabled from the vSphere Web Client and greyed out from the DCUI.
I discovered that the symptom was caused as the permissions for the DCUI user were removed from the ESXi host system. In order to resolve the issue I performed the following on the ESXi host system.
1) Connect to the ESXi host system using the vSphere Client.
2) Select the ‘Permissions’ tab.
3) Right click and select ‘Add Permission’.
4) Select the DCUI user and assign the Administrator role to the user account.
5) Select ‘OK’.
Following the above change I was able to modify the Lockdown Mode from the DCUI and then manage the ESXi host system from the vSphere Web Client.
Deans Blog 