Ok, went to my friend's house (he has a 60GB like me), and it worked fine there.
There's GOT to be an option I've overlooked or something. I've tried the 24fps 1080p one, atrac & wmv are already enabled (not that they should have any bearing on a BD), and I've reset to factory defaults twice... I'm wondering if not having the original hard drive might have done something (was originally planned to be a 120GB drive for 360, but after flashing sector 16 I found out my drive wasn't supported. I believe I restored sector 16 to it's original state before throwing it in my PS3, however I'm not certain. I haven't experienced any other problems with my PS3, and I'm fairly certain that if this was causing the error, it'd do more than preventing just one BD from scanning).
My system seems to refuse to acknowledge the disc; no other BDs have a problem (out of the 16 or so titles, including the other 4 Harry Potter movies that came with the set).