So my editor exported my finished file for me. He sent it to me in USA. I then needed to add some titles to it, so I imported it into FCP 6 and added my titles and tried to export it. I tried as PRORES 444 and also as H.264 but neither worked.
My scratch disk says . . .
45.5GB on Macintosh HD
and Minimum Allowable Free Space on Scratch Disks : 2047 MB
Any help would be hugely appreciated!