I'm sorry, but I still cannot reproduce your problem. Please check the configuration of your virtual directory. Make sure that the virtual directory points to the correct physical path. Please also make sure that the virtual directories for the projects giving the error do not inherit some wrong permission settings from a parent node in IIS. Are you getting the same problem when browsing the site, or only when administering it? Is it only happening for the sample sites that come with Sitefinity or other projects as well? Could you please tell us what actions you took before the problem occured so that we can investigate it.