Hi, i am new here... i just wonder why some manga cannot be download??

Well, the downloads you do see are already more than there should be.
rule#1:

We are an information site and NOT a download site.

To find the scanlations, you probably just need to go to whatever group's site.

[img]http://myanimelist.net/createimage/SirGir.png[/img]

Because it's a manga info site not a dl site. You have to look and search yourself.

And if it's reported on this site, it DOES exist. Don't think that we're trying to trick you. If someone reported a fake release though...then we'd get the knife and the rope out...

Here's a hint for most of your problems: IRC

A just ruler amongst tyrants