This property offers a critical section to access the property SecurityDescriptor.

COM is able to access the COM methods implemented by TJwServerAccessControl from different threads .To avoid race conditions these methods are secured by a critical section. 

If you access the property SecurityDescriptor directly.you need to use this critical section in this way: 

...
  IA.CriticalSection.Enter;
  try
    access here IA.SecurityDescriptor
  finally
    IA.CriticalSection.Leave;
  end;

The JwXXX functions (like JwGrantAccessRights) are thread safe. 

Do not free this property!

TJwServerAccessControl Properties