You could go to the link below and download "XP_Fix.EXE".
"This installaton 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.
We recommend that you download this file and save it to your desktop or to another location where you can find it. Double click on the file to run it once it's downloaded. If problem reoccurs in the future, simply re-run this program".
Here's another link to basically the same fix to download.
Another fix some have used is to do a search for autoexec.nt You will probably find it in C:\WINDOWS\repair. Copy and paste it into C:\WINDOWS\system32.
The 2 links below explain what may be causing the problem (Malware).
Hope this helps,
Anyone help - when I type 'command' in RUN I get the following error message
16 Bit MS-DOS Subsytem
C:\WINDOWS\SYSTEM32\AUTOEXEC.NT. The system file is not suitable for running MS-DOS and Microsoft Windows applications.
Pc running - Windows XP Pro.
This is the only problem Ive encountered with this message. Any help appreciated thanks in advance.