This is most likly due to not having the mesh settings correct. I managed to duplicate the problem and it occured only with my skyboxes and/or smooth turned on. In map properties the mesh size needs to be set to 0 or the build needs to be done with create mesh flag set. This seemed to fix the problem. Frederick_Lim gave a very good explanation of this in another thread. It does mention this in the manual under new features, however you need to make sure you have the 7.05 manual. I had the 7.04 manual which does not mention mesh size. It would be nice to see a tutorial or a discussion on what these mesh settings should be.