Hmmm, looking at the other two threads you made about this, you get it whenever you change the unit graphics, no?
My guess is you're using something like MS Paint to put in the images. That won't work.
There are a few things about the units.gif (and all the other GIFs for that matter) you should know:
- The GIFs use a specific color palette, if you change it (or the image editor changes it without your knowledge) changes are things will look odd.
If you have a more advanced image editor it's a good idea to save the palette. That way you can load the palette for all your civ2 graphics you create. Use the palette of the units.gif, that's the palette Civ2 itself uses for all its graphics. That also means if you change the units.gif palette, all Civ2 graphics will be affected, while if you change the palette of any of the other graphics files, they'll just end up looking like ****.
- Secondly, and most importantly. The GIF images must be in GIF 87a non-interlaced format. A lot of image editors will allow you to choose among the different formats, but MS Paint doesn't and saves them in the wrong format. That's why Civ2 crashes on you.