Programs that manipulate volume blocks during the boot process, either directly or by using the FSCTL_MOVE_FILE control code, may cause data corruption or data loss in Windows Vista and in Microsoft Windows Server 2003. In this case, a drive volume may become unmountable. Additionally, you may be unable to start Windows.

Note: Defragmentation programs that perform tasks early in the boot process, before the Autochk.exe program finishes, are one example of the kind of program that may experience this problem.