Permissions default to EVERYONE/FULL CONTROL on shares. Some new NT/Win2k users will eventually see that their...
c: drive is thus exposed to the world, and often change it to (usually) ADMINISTRATORS/FULL CONTROL, or something similarly restrictive.
However, this removes SYSTEM from the permissions list, "leaving the System account without the ability to manage some system resources, such as the paging file on the system root" (a/t Microsoft in Q259151), and generates some puzzling error messages at startup.
If you see a message like, "The system has no paging file" at startup, this is a good place to start looking.