i've checked my ssh and git remote -v
or ssh -T git@github.com
and all worked fine, and i was still getting the error. the reason was because i initialized on the wrong working folder. meaning, after you mkdir for your working area, you then supposed to init in the current folder you are. and i made the mistake of going into the folder of the working area, and then git init it, and thus git didn't know where is my working area.
example:
this is the mistake:
current-dir$> mkdir new-git
current-dir$> cd new-git
current-dir/new-git$> git init new-git
correct procedure is:
current-dir$> mkdir new-git
current-dir$> git init new-git
it might help to check.