Work methodically and follow the steps Steve laid out. Your project also seems to be rather heavy, so I’d first separate the comps in a sensible order and create separate projects. Getting rid of unnencessary footage elements etc. might do wonders and at least some of those separated projects are guaranteed to render flawlessly. When that’s done, sifting thru the rest and finding the problems should be much, much easier.
Mylenium
[Pour Myl