ok!

so i'm cutting together a feature length film and everything has been going more or less, swimmingly.
i bring all of my scenes into a master timeline and one particular scene simply doesn't display anything.
It's been renderd so i'm not getting the 'unrederd' blue screen.

Quite simply, the squence plays just fine when it's all by itself, but when it's brought into this master timeline, it only displays the first shot and then crossfades to black (where it should crossfade to another shot)
Once the scene is over, it displays again normally.

Has the Alpha mode for that one scene been accidentally changed?

beleive it or not... i re-nestled the scene into the master timeline and now works.

i've no idea what the problem was but it has apparently fixed itself.

I'm finding that FCP 6 tends to "forget" render files and get confused and use "obsolete" renders often, requiring BIZARRE intervention. The software is becoming more problematic with every major iteration, from a "I just want it to work" position.

For example, I've colour corrected two clips and put a cross dissolve between them. Later I've removed the cross dissolve and replaced the first clip. Upon playback, FCP still thinks there is a cross dissolve on the first bit of the second clip.