Resolution:

Logged into SQL server

Open MSSMS

Expand databases

Expand vCenter Database

Expand tables

Right-click dbo.VPX_ACCESS

Select Top 100 Rows

Check if the accounts or groups are present in the PRINCIPAL column

MAKE SURE YOU HAVE BACKED UP YOUR DATABASE PRIOR TO ANY CHANGES.

MAKE SURE THAT YOU ARE DELETING THE CORRECT ACCOUNT, THERE IS NO WAY TO RECOVER THE ACCOUNT WITHOUT A PROPER BACKUP/RESTORATION.

Single Account/Group

DELETE FROM [VMware].[dbo].[VPX_ACCESS] where PRINCIPAL='USER-OR-GROUP-TO-DELETE';

Multiple

DELETE FROM [VMware].[dbo].[VPX_ACCESS] where PRINCIPAL LIKE 'USER-OR-GROUP-TO-DELETE';

Restart Windows services

VMware vCenter Inventory Service

VMware VirtualCenter Server

VMware VirtualCenter Management Webservices

Log back into the vCenter

Check that the account or group was removed from the permissions tab

Note

I can't stress enough a proper and full backup prior to any mayor changes to your database.