When I use the orbit command I have had conduit and cable tray disappear and the only way that I have found to get it to reappear is to undo back to before I used the orbit command. This has happened in 2008 as well as 2009. Any thoughts?
I have tried that and it does not work but since then I have found that if you change to 3-D wire frame from realistic and back again the conduit or cable tray reappears. Saving your drawing seems to do the trick sometimes also.