Objects not showing up in render (but shows up in viewport preview)

Here’s something that’s not happened to me before…strange.
I have a number of objects (characters) that will show up in preview but not when I actually render (F12).
I’ve tried “unrestricting all” with “W” but nothing seems to work and the visibility is turned on in the “outliner”.
Please help.
Thanks.

SDCDM physics.blend (4.78 MB)

It works fine for me, I think. When I compare the render with live and solid views I don’t see a difference, short of there something being in the background that I don’t see. It could be a UI settings’ problem.

http://www.pasteall.org/pic/92038

the same happen to me but only when i switch computers ,for example a file will render ok in my computer but in my laptop or the computer at work the characters will dessapear!! any help ? i am usng blender version 2.67 and xp

You haven’t even included a link to your blend file for review ?