But there was a problem - it got so far (about 4 GB) and then had problems with getting endless bad pieces. Hmm, delete the .torrent and try again. It reckons that about 1 GB was ok, and proceeded to download about 3 GB again.
Again the problem. Piece 1023 was proving particularly problematic - were some seeders 'poisoning' things? Is there a problem with the memory card?
Let's try it on the main PC. Copy what I've got.. yawn, this is taking a while.. ah, ok. Get the .torrent file again, let it check what is already there - no problems, phew!
After a while... download finished.
OK, let's do an MD5 of it, then copy it to the memory card and MD5 it there - that'll show up any problem with the card.
After a while... 'file too big'.
I'd forgotten FAT file systems can't cope with large files. Oops. It had been trying to save pieces, and either failing to do so or getting the wrong result when it tried to read them again, and complaining about the data being bad rather than the actual problem.