Error msg when installing .exe file

I have started getting this error message when installing or running a .exe file:  

     c:\windows\system32\autoexec.net.  The system file is not suitable for running MS-DOS and Microsoft Windows applications.  Choose 'close' to terminate the application.


(I should also note that the header on this error message says:  "16 bit Windows Subsystem.")


Action I have taken:  I went to the display properties/"Settings" tab and clicked on "16 bit" color setting and tried to install my file.  Then I set it back to "32 bit" & tried to install...rebooting between each setting.

My computer is:  Windows XP, Version 2002, Service Pack 1       Pentium 4

Thanks for any help.  Allie