Border render in mesh I'm rendering a movie in cycles.
When I'm rendering an object (2 objects copied with AltD), a part of the mesh disappears, determined by angle of the camera. 

it acts like a render border, but it only effects a "vertex group" of the mesh. The mesh doesn't has any actual vertex groups. Or any of that kind (looked at mesh-data in the Properties editor). I can't find any strange settings.

This is shown in the render view as well as in the viewport. And only when it shows the render view. I tried the internal render. But then the whole render is inexplicable

I can't give a picture of the problem, because I have confidentiality. and can't reproduce the problem because I don't know how it came there.

(blender version is 2.66 or 2.69, same problem on like 30 computers (just with the 0, but its coincidence), re-saved with new name multiple times
This is a bit unlikely because your mention of "vertex group", but a problem most similar to "render border" is when active camera's Clipping distance is too limiting for the scene's size. For example, the following scene is using default camera:



Lower-right object is of regular size, and intersects the camera's Start/near clipping distance. While upper-left object is 10 times larger and bumps into the camera's End/far clipping distance.

If this is the case, relevant settings you need to adjust are in Properties window > Object Data tab > Lens group for the camera object.