@fanbaby:I vaguely seem to recall that the registry uses a technology called OLE Structured Storage, and that it is the same technology used by MS Office documents until they changed to the zipped XML format.
Its not like this issue occurs every other day, but i see it once in a while on multi-user machines. I have never had the issue on my own single user machine. So it seems to me that the dangerzone lives on shared machines. I guess, that is nothing in windows that prevents a program from alter the user profile for other users, and that might be the root cause.
Sometimes a user profile just stops working. In those cases the solution is a simple as deleting the profile and log on again, as other has said in this thread.
In my current case i get a "Windows cannot copy file \\?\C:\Users\Default\ to location \\?\C:\Users\TEMP\. This error may be caused by network problems or insufficient security rights. DETAIL - Access is denied." when a new user tries to logon on. In this scenario, its most likely best to scratch the OS since some crutial permissions has been messed up. BTW google returns 14.400 results for that error message, and 550.000 results for "Windows cannot log you on because your profile cannot be loaded" so am i not alone in having this issue.
In the current case it is and 2012 AD controller and the errors has occurred right after trust was established with another domain.
My point is that there should be some tool that should be able to validate and repair the user profile and related settings/files/directories.
I guess there is a reason for the Win8 reset profile thing.
UPHC is built-in since Windows 7 - you can tell by the presence of eventID 1530 entries in Eventviewer.
Most profile problems I see in our enterprise are linked to the fact that we're in a rather awkward migration phase - users in one forest, machines in another (forest trust, CFRP & GPO enabled).
Every now and then, a hiccup in the trust connection 'll throw a spanner in the works.
Or some goofball changing user GPO settings without proper testing...
Other than that, customized security templates (the secedit ones) from the days of yore still present in your environment can and will seriously screw up the OS.
My credential store got hosed on my primary machine. It prevented any Windows Store app that required logging into Xbox Live from running at all. I ended up having to create a new user profile. This is was the first time I've ever had a Windows user profile get hosed on me. Based the number of issues users have had with Windows Store apps, as reported on http://answers.microsoft.com, it seems that the WinRT application stack is what is fragile. BTW, I was appalled that the "official" Microsoft resolution for issues related to Windows Store apps is to "refresh" the machine. I have tons of desktop applications installed and use only a handful of Windows Store apps, so I wasn't about refresh my PC for such a trifle.