This problem could be in the Single Player Game in the middle of Return to Napali. If you want to load a game in complex situations, the game crashes. This problem is solved some years ago by some unreal players. You have to change the unreal.ini. This worked for me.

Open the unreal.ini with editor and find the Engine.Gameinfo and the entry for MaxPlayers. Change the value of MaxPlayers from 16 to 32 (or more).

Thats it. Thanks to Gendor in the forums of beyondunreal.com.

Thank you, and Gendor too!