I've got the same message as well and I live in Australia.
I think it has to do with the latest hack fest. Sony changed a lot of the PSN anti-hack program etc... and for the Japanese PSN, I think they blocked every players who tries to use Japanese PSN OUTSIDE of Japan.
What a shame... I mean I still got some credit left in my account and I got like 3 Japanese PSN cards unused and this happened??
Anyway, I'm not sure so we'll see if anyone else have same problem.
EDIT: I've just contacted one of my friend in Japan and she was able to use to PSN

I guess its only for those who's living outside of Japan.