Gunbuster and Diebuster Blu-ray requires more recent firmware?
I picked up the Gunbuster vs Diebuster Blu-ray set yesterday, and was surprised when they didn't play on our Sony BDP-S300 Blu-ray player (it wouldn't even load the disks). Then I tried them on my ps3, and they booted up perfectly. I've always kept my ps3's firmware up to date, so I thought that that might be the issue, as I've never updated the firmware on our standalone Sony BD player (never had a problem getting it play any BD movies before, so I just never bothered...). So once I updated it (to version 4.30), both movies play perfectly fine now it.
I'm not sure how up to date the firmware needs to be for the movies to boot up. But we bought that Sony BDP-S300 around this time last year. So at the very least, whatever firmware it was running with the factory default, wasn't recent enough.
On a related note, the Freedom BD set, worked perfectly fine on the old firmware, so Bandai Visual must've done something different with the Gunbuster set that requires more up to date firmware installed on your BD player.