Well thanks everyone for trying to help. It seems like some people get it to work no problem and some people can't.
I haven't been able to see any common themes here to differentiate the two cases so I have no idea what's going on.
I'll try re-transferring with flashfxp rather than filezilla and see if that works. I'll try using a different ftp server too, just to see what happens.
Forgot to mention I have a slim PS3.
I've transferred it again with flashfxp and no dice.
I've only got it to successfully launch ONCE, and that was immediately after I had just completed transferring Little Big Planet from BD to the internal drive with OM 1.16.