try that file and reboot
This installation program will reinstall the missing or corrupt Windows XP system files command.com, autoexec.nt and config.nt. The absence or corruption of one or more of these files causes a "16 Bit Subsystem" error.
XP_Fix.EXE by TRF Systems, Inc.
You have possible spyware that could be deleting these files
Running Audit on my computer showed that a program called
WINDUPDATE.EXE (not WINUPDATE.EXE) was deleting my Autoexec.nt file on boot
up. If I replaced the file it would delete it again. Go to \Program
Files\WINDUPDATE folder and delete it!
Go to your registry and delete anything named WINDUPDATE. Put the Autoexec.nt
file back into your \system32 folder and all is well! This was definately the
problem here and I bet most everyone has the same nasty bugger, WINDUPDATE.EXE
on their infected computer.