Just got my Limited Edition for Crysis 2 from a local store two days ago.
(Manufactured in Singapore,because there's a tag of "M18 BFC,Singapore" tag on it.)

But I only have a Japanese PSN account,I still entered the bonus code(In cap letters.) in the place where you can use your 12-code thing on the PSS homepage of PS3.(JPN ver of PSS)

The result comes with "invalid" in Japanese.

Can anyone help me about this,any answers will be appreciated.

I tried everything I can do to active the code:
Type in lowercase letters.
Lowercase and cap letters hybrid.
Googled for "How to active Crysis 2 Limited Edition code for PS3" and read tons of results I got.(No tuts for JPN version of PSN account yet.)

Answers to all the minimal questions you probably will ask:
Is it the retail version of the game for PS3,you sure no pirated?
Yes,I'm sure.

Have you ever tried to register a US PSN account to play?
Yes,but the site(PSN US's site) to confirm some final stuffs is doomed before I can complete my registration.

Does your Japanese PSN account work on Multiplayer mode of the game?
Yes,it even comes with 1 red bar and lagness.

And please fix the lag problems for PS3(I'm using slim version.)

Download codes are usually region-specific, so the Japanese PSN store doesn't recognize the code because it's either for the US or the Singaporean version - it's not clear from your post which you have, but either way, I'm guessing that's the problem, and there's no way around that.

By the way, you may also not be able to play the DLC maps if you download them from the JP store, I'd at least try to confirm that they're going to work before you pay for them. I've had this problem with the US version of Resident Evil 5 and DLC from the Swiss PSN store. I can play online with the US version of the game and a Swiss PSN account, but it doesn't recognize the DLC.

There is just on way to fix that.

Make a singapore psn account, sign with it and use your code.

That is what EA did tell when I mail them for the same reason and it worked.

Download codes are usually region-specific, so the Japanese PSN store doesn't recognize the code because it's either for the US or the Singaporean version - it's not clear from your post which you have, but either way, I'm guessing that's the problem, and there's no way around that.

This. (Unless stated otherwise)

I'd do what the dood said in the above post. If not, contact EA support I'd assume.