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.