Roughly translated, tmaster has concluded the following:
"FW2.50 not start in the BD-J.
Upgrade to stop so we can update orz"
I don't know if Bu-nyan is saying its ok to upgrade or not.
Update: I can confirm that bd-j don't work with 2.50. I tried it on my brothers ps3 and it gives me an error. good thing I still have mine at 2.43 to play java.
Why sony stopped I don't know.. maybe a hack, who knows?
Note: FYI, although most of the PS3 Devs are sleeping CJPC said the following on IRC: "It probably is on, but they may have changed it a bit.. possibly to only work from a pressed bd-rom or some bs, which, still makes 0 sense. bd-j functionality is CORE for any bd player.. at profile 2.0 that the ps3 has (or 1.1, can't recall) so bd-j is not off, something just changed with it."
That being said, it may explain why Bu-nyan and others are reporting BD-J as not working... when...