The hole packaging is a mess...
Be sure NOT to add an rtf-file into the zip-file, if it's unnecessary. Use a .txt-file of notepad (or whatever it's called on a mac) instead. In this case it's completly unnecessary to add such file, so just don't (use the "/maptitle" command instead).
As far as I know (since no other maps have it), any mac file like ".DS_Store" shouldn't be in the zip-file, no matter what. Why? because any computer shouldn't have any problem starting up the map without those files (this also counts for the "_MACOSX" folder).
If this is untrue, then I wonder why no-one was complaining about it before.
Also, be sure to use ".jpg" for loading-screenshot, because it cube engine (2) isn't taking any .png-file for such task (don't ask me why). However, some editions ago it is accepting other resolutions than 256x256, so a resolution like 512x512 is acceptable (not recommended tough).