Hi I thought i'd upload this tgd file in case it's any help to you in squashing this bug once and for all.
Hmmm I don't think this is going to be any help after all. I've just hit render again without altering anything and it's rendered ok, without any red. Strange
It does seem to be a semi-random/intermittent problem. I think we have enough test cases to track it down for now though.
Thanks!
- Oshyan