I'm not sure what it means. It looks like it would be associated with 3D rendering, but you say you were using the software mode.
Is it possible you have a corrupt saved game? Can you restart the game without the error?
I can send you a bunch of saves from playing the game on Windows 98, but I don't know whether they'd work on Windows 7. You'd have to ask about how to use the saves in the Hints forum. Windows 7 undoubtedly puts saves in a different location than Windows 98 did.
I've uploaded the saves to my dropbox account in case you want to try them.https://www.dropbox.com/s/dw0d5wia258xc4d/MotD.zip