Your originally posted this a few days ago:
http://gbatemp.net/index.php?showtopic=77703
Please do not double post the exact same question. If you need to change something in your original post like adding what type of Flash kit you are using, use the "edit" feature of the forum. Double posting only causes more clutter and confuses people who are replying to your original post.
Now...
Can you get on Nintendo WIFI with any other Game, ROM, or Homebrew?
Is your router set up correctly?
Can you verify that your ROM is a good dump and not a hacked, patched, altered dump from some random corner of the Web? Basically do you trust the source you got it from!
We can not start to debug your problem until you add more information. There is a chance it is user error (the settings) or perhaps the ROM is bad or requires some type of patching to work online. If I recall correctly most of the Pokemon games have required patches to function on Flash kits in the past. That isn't to say this one requires it, but perhaps it does wth the type of Flash kit you are using. You might be better off writing a new post or pointing others to your original post in the Flash kit section of the forum.
Respond with the answers if you can and I will try to help you.
-AW