If your Natural Log for DOS won't display in full-screen under Windows 98/Me/2000/XP
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 If after you update to Windows XP Service Pack 2, you can get an error message when trying to run any DOS-based program [such as Natural Log 7]: C:\Windows\System32\Autoexec.NT. The system file is not suitable for running MS DOS and Microsoft Windows applications.
Choose ‘Close’ to terminate the application.
Click Here to go to Microsoft's support site for the solution