The active language was the default "en".
My site has a lot of things: 10 courses with sounds, flashes, 6 online glossaries with 3000 words each. 6000 quizzes. Most of the contents (including quisses are translated into 5 languages (three asain languages) using multi lang-filter.
So, I deleted used modules, reduce numbers of blocks. Turn off Japanese version. Also, I asked my server to increase memory limit up to 16M. Then I turn off all filters and turn on again only auto-link and multilingual.
And It finally works again.
Thanks for your reply, Eloy Lafuente. Now, I'm very careful not putting too many things in the same pages.
Dinh Lu Giang