[Vincent Sheehan] “info from File Inspector: AAC, Stereo (L R), 44.100 kHz
H.264 Decoder, 720 x 576 (1024 x 576), Millions. It was created by a post house from a an HDSR master.”
FCP 4.5 will not understand H264 as it is old software. No version of FCP will be happy to edit H264 native so the file needs to be converted to an editing codec. Software like MPEG Streamclip will do the file conversion
https://www.squared5.com/svideo/mpeg-streamclip-mac.html
If your drive is fast enough, you could make it Uncompressed 10 bit with the same pixel aspect (720 x 576) or at a pinch DV codec (yuck). The audio is the wrong sample rate so it needs to be converted to 48Khz PCM.
H264, although common now is not a universal codec. It would have been better to make the file in an edit codec from the start.