We have put in a bug report regarding this issue. Meanwhile you can delete the contents of that folder in Windows Explorer rather than via the SecurityCenter interface. But make sure it's just the contents of the folder you delete not the folder itself.
First you have to disable Access Protection.
Double-click the taskbar icon to open SecurityCenter
Click Navigation (top-right)
Click General Settings and Alerts (left)
Click Access Protection (below)
Uncheck that and click Apply
Now open Windows Explorer ('Computer' for instance) and go to Tools/Folder Options/View and check 'Show Hidden Files & Folders' and click Apply/OK
Then go to C:\ProgramData\McAfee\VirusScan\Quarantine (assuming this is the 'C:' drive, if not alter that to match)
Using the Edit button Select All to highlight
Click Shift/Delete simultaneously and OK any prompts
They should be gone. It may take a while if you have a lot.
I realise that you may know most of this but thought it best to post the full intructions for anyone else reading it.
Re-enable Access Protection afterwards.
Thank you for all your help and patience. I wish more people were like you.
Thank you once again.
Thank you and glad to help ;-)