I usually render at extremely high DPI and resolutions so I can get a good print out at poster sizes at the local print shop.  I do test renders poretty much at default. This problem seems to be occuring at any setting or resolution.  I tried at base normal settings and the same thing happened.  I am also noticing a few other odd things in the last couple of projects.  First, I seem unable to copy some objects.  I wanted to try and isolate the problem so I created a brand new document and tried to copy the model to it, however after selecting her groupm I do not get the copy option from the edit menu, it is greyed out.  This also happened with the battlesub.  I end up having to export the individual object groups and then import them into the new document.  Also I have noticed that if I get too close to an object, it disappears.  The only way to prevent this from happening is to reduce the distance to near plane value.  In the render I am having the problem with, it had to be set all the way down to zero.  This never happened before I updated to 6.21 so I am assuming it is probably a bug.  Normally I can det around it, but in this render I just can't shake the problems.