KF rendering
1. Your red bar is probably not at your current frame. If you don't use the
"Use KF" button to extend VP to use your entire KF sequence, this is a common
goofup.
2. Background images set in the Background dialog outside of VP aren't used by
VP at all… VP is a compositing system independant of the background method
outside of VP (which is a mini-VP in and of itself).
– G