FCP7 export problems - black frames and text irregularities

Question

I'm on FCP 7.0.3 and have recently started editing stuff from my new Panasonic HDC-HS900.
I started a small project just to get to grips with the new workflow and realised that I had made the mistake of trying to import .mts files. However, I found a plugin from Panasonic's website which allows this but editing with the imported files is a nightmare because FCP starts running so slowly that it is impossible to make any kind of precise edits - the scrubber bar jumps all over the place and moving it forward one frame with the arrow keys takes about three seconds.
So, I realised my mistake and having discovered that using ClipWrap circumvents all these problems, I devised a new workflow and resolved to stick to it.
The only problem is that I showed the test edit to my girlfriend and her parents and despite it being full of bad stuff (I mean very rough edits caused by the slowness and audio problems that I couldn't be bothered sorting out also because the process was so frustratingly slow), they all liked it. So, whilst I would like to consign this experimental disaster to the bin, I need to at least iron out some of the problems so that I can give my girlfriend a copy which does not look quite so awful.
So, after labouring through this excruciatingly slow process, I try to export the finished thing only to find that the opening ten seconds, where I have used a slow motion sequence (which, ironically, is not an .mts file - it's a 10s .mov file I exported from FCP in order to convert it from 50p to 25p slow motion without losing frames) and a bit of text which dissolves in and out, there are a few single black frames and the text disappears momentarily several times.
Everything else is fine (apart from the awful edits!).
Having now left FCP to render the whole sequence, I managed to inspect it frame by fram much quicker and on the timeline it looks exactly as it should - the edit itself couldn't be much simpler; two layers - one text, one .mov file. dissolve the text in for one second, two seconds later dissolve in the .mov then a virtual reverse process. What could possibly go wrong?
Anyway, I have deleted all the render files and I am currently waiting for the sequence to re-render - estimated time: two hours.
All I want to do is wrap this junk up so that I can start a proper project.

Answer 1

I'll have to respond in an unordered fashion, just to try to make sense in my reply.
I was using ProRes 422 HQ because I found three options in ClipWrap and had to make a quick decision based on two minutes research and having found by trying it that 422 HQ files were only about 25% bigger than 422 files, I figured I had nothing to lose - especially as the workflow I WILL BE employing does not require permanent storage of the files and I now have 1TB external space for media archive storage and over 600GB internal space for ongoing projects. I might as well use the highest quality.
The reason I suspected the rendering files is that they were being used by FCP in the export of the project - evident in the fact that it takes almost three hours to save an unrendered sequence vs about six minutes to export a rendered sequence. Therefore, being unaware of the inherant problem you mention, I think it was reasonable to guess that a forced re-rendering might have sorted it out.
Yes, with 20/20 hindsight, it might have been quicker but, again being unaware of the issue you mention - which I shall have to look into - it seemed like a small problem which ought to have a had a simple answer. But now I know better.
I have, incidentally, discovered that all the dissolves I inserted have very similar problems.
And, to answer your first point last, I have already gone down that path - I'm just waiting for the results.
Could you perhaps point me at some article where I can read about the inherant problems of H.264, please?