Why do I receive an error when I attempt to run a 16-bit program under Windows NT?

A. When you attempt to run a 16-bit application under NT, you might receive the following message:

Application popup: 16 bit Windows Subsystem : An application has attempted to directly access the hard disk, which cannot be supported. This may cause the application to function incorrectly. Choose 'Close' to terminate the application. 

This error is typically the result of an invalid entry in the command.com, autoexec.nt, or config.nt files, which NT maintains for compatibility with 16-bit applications. To resolve this error, restore the default versions of these files from the NT installation CD-ROM by performing the following steps:

1. Run cmd.exe (go to Start, Run, and type cmd.exe).
2. Navigate to the %systemroot%\system32 folder by typing

    cd %systemroot%\system32 

3. Rename the current command.com, autoexec.nt, and config.nt files and append the word "old" to the filenames by typing

    rename command.com command.comold
    rename autoexec.nt autoexec.ntold
    rename config.nt config.ntold 

4. Navigate to the i386 structure of your Windows installation path (e.g., d:\i386) by typing

    cd /d d:\i386 

   (the /d lets you change the drive and path at the same time).
5. Expand the original files from the NT installation CD-ROM by typing

    expand command.co_ %systemroot%\system32\command.com
    expand autoexec.nt_ %systemroot%\system32\autoexec.nt
    expand config.nt_ %systemroot%\system32\config.nt 

6. Restart your computer, and run your 16-bit application again.