SharePoint 2010 auditing policy for folder content type causes error

Question

if I want to add an auditing policy on a folder content type I get an error that the content type "Folder" at "/Shared Documents" is sealed.

Does this mean that it's impossible to add an information policy on a folder content type?

If yes why is this the case?

Thank you in advance

Regards

UPDATE:

Answer: http://social.msdn.microsoft.com/Forums/en-US/sharepoint2010general/thread/1aff3461-c697-4228-8d37-567b60ffd705