For instance, did you change the name and save name of the map in the mission info?
Yes
One other thing... The description document for your map should be titled as your map's name. I don't think a 'description.txt' will appear on the map preview screen.
This is the description document:
Title: Deep Freeze Circuit
Author: Deep Freeze
A basic racing map. Deep Freeze's first map, made the day after he learned how to use Mission Editor.
Btw, just for fun, I wanted to post this for you. This is the preview file (deepfreezecircuit.jpg)
Do you like it, for a first map?
Edit: AHA! Realized I need to use PNG for map preview.
BTW, yes, the yellow checkerboard texture is in the zip (Checkerboard_yellow.jpg).