running IIS on windows 7. Using lusrmgr, the IIS_IUSRS group is empty. When I attempt to add IUSR to that group, the system says IUSR cannot be found. But when I use windows explorer, properties, security, I am able to grant IUSR rights to a web application folder. Why would the IUSR profile not be found using lusrmgr, but is found when granting authority thru windows explorer? thanks,

I see that IUSR is a "built in security principal". When granting rights to a file or folder, the built in security principal is one of the category of users that can be specified. When adding a user to a group, a built in security principal cannot be used.