Yesterday I helped my father to install his new computer with Windows 7. For several reasons I shall not mention, it was in the best interest to take the hard drive of the old (broken) computer and copy all the data from it to the new. What he (and me) wanted was to keep all the settings and other stuff and just reinstall his programs. That meant copying the entire AppData folder under his user account in addition to his normal files. During this process obviously all files had kept the old SIDs, and as they weren't matching his new SID (on the new computer) I was having problems accessing the files. Lots of stuff didn't work. I was getting "No access" messages left and right when I tried to change the permissions of those copied files. That is when it dawned on me that even though his user account was registered as an administrator, it wasn't able to change the permission bits on those files.