16 bit MS-DOS Subsystem "illegal instruction"

[Brian]

I keep getting this message when I boot up my computer
Title Line "16 bit MS-DOS Subsystem"
C:\WINDOWS|system\WINSET-1.exe
The NTVDM CPU has encountered an illegal instruction.
CS:0536 IP:0111 OP:63 61 70 3a 45 Choose "Close" to
terminate the application

What is this and how do I fix it? I chose "close". I do
not notice anything that does not work.

thanks