Err Msg: The WIN16 Subsystem Was Unable to Enter Protected Mode

• Microsoft Windows NT Server version 4.0
• Microsoft Windows NT Workstation version 4.0

SYMPTOMS

When you attempt to run a 16-bit Windows-based program at a command prompt using the START command, you may receive the following error message:

   The WIN16 subsystem was unable to enter Protected Mode, DOSX.EXE must
   be present in you AUTOEXEC.NT and present in your path.

CAUSE

This error message occurs when all of the following conditions exist:

• The /separate switch is used with the START command.
• There is a .pif file for the program in the path.
• The .pif file references custom Autoexec and Config files that do not load Dosx.exe or Himem.sys.

RESOLUTION

Rename the program's .pif file. Change the .pif file name from <Program>.pif, where <Program> is the executable file name of the program, to <Program>.xxx. Make sure to search for and rename all instances of the <Program>.pif file.

MORE INFORMATION

The START command is a command-line tool that starts a separate window to run a specified program or command. It is frequently used in batch files. The /separate switch starts 16-bit Windows-based programs in separate memory space.

When you use the "START /SEPARATE <PROGRAM>.EXE" command, the path is searched for any instances of a <Program>.pif file. If no <Program>.pif file is found, Windows NT loads the _default.pif file and then runs <Program>.exe. This behavior does not occur if the /separate switch is not used, nor does it occur in Windows NT version 3.51 even when the /separate switch is used.