I have this morning clicked onto a couple of programs on my desktop and got a window opening: 16 bit windows subsystem...this says ...C:\windows\system32\autoexec.nt. the system file is not suitable for running MS-DOS and mircrosoft windows applications. Chose 'close' to terminate the application.
The is then a close and ignore button...clicking on both closes this windows and nothing happens.
This was working fine until I downloaded an automatic windows xp update.

The same thing happened a few months ago and when I couldn't solve the problem I ended up reformatting and reloading everything.