Dave
As a rule I always transcode to one of the ProRes codecs, but for what ever reason, these 4 clips were rendered incorrectly, however if you read my original post, the issue is not with the H.264 part of the workflow, it’s final cut not being able to render a prores clip (the one roundtripped back from color)!
This is the error message I get when trying to render in Final Cut.

The clip details are below, which clearly show this as a ProRes clip. Annoyingly enough, final cut handled the H.264 element of the workflow just fine, so your H.264 question count has just gone down to 799.

I know to fix this I need to go back and redo the image sequence and ripple the change through. The question was raised because Final Cut was bitching about its own ProRes Codec.
Regards
Declan Smith
https://www.madpanic.tv
FCS3 / After Effects CS5 / Combustion / Canon 7D / Canon XL2