I have also made really big structures and when they're big enough, the beams just disappear. And when I remove some of the beams the problem goes away. So it really seems, there's a limit in the engine (that should be removed right away http://www.pontifex2.com/iB_html/non-cgi/emoticons/smile.gif" border="0" valign="absmiddle" alt=':)'>)