[PyMOL] dissappearing model

[Kelvin Luther]

Hello all,

I was hoping someone could tell me what I am doing wrong.  I have on many 
occasions produced nice pictures of my models using pymol, some for 
publication.  However, I occasionally run into the problem where I load 
pdbs or run a .pml file, and the picture on the screen looks like pieces 
are missing.   As I rotate or translate the model pieces come into and 
then out of scene.  Needless to say, I don't want this to happen, I cannot 
have pieces of my model dissappearing, and it is making it extremely hard 
for me to work with a ligand I am currently trying to position.  Is there 
something that I have set incorrectly as far as the display?  This is 
particularly bothersome when I have a surface representation as there are 
pieces of the surface that dissappear, and it looks like there is a hole 
right through the protein at that point.  Rotate some more, it fills in 
that spot and another hole appears elsewhere.  Thanks for your time.

Kelvin Luther