another thing you might want to know is that sometimes a bad program holds a resource (could be a file or something else) and doesn't want to let it go. In that case, if you want to access that resource (with admin privilige), NT will give you the same error. So you can try reboot or uninstall the suspected program or whatever to get the control back. In most cases when this happens, it's the program to blame instead of OS (although the OS can be a little more robust).