some applications error message

When I try to run some applications or (e.g., an old game), an error message box pops up, saying:
16 bit windows subsystem: C:\WINNT\system32\autoexec.nt. The system file is not suitable for running MS-DOS and Microsoft Windows applications. Choose 'Close' to terminate the application.

Login as Administrator or with an account with Administrative privileges. You must be in the Windows Safe Mode to login as Administrator in Windows XP Home Edition (press F8 several times just as Windows is about to start and choose Safe Mode fromt he resulting menu). You may need to enable view hidden files and folders in the Windows Explorer, Tools, Folder Options, View. I also disable Hide file extensions... To fix the problem, use the Windows Explorer to copy autoexec.nt from C:\>Windows\repair to C:\>Windows\system32. To prevent it from happening again, right-click the file, Properties, check Read-only.