You will receive the below dialogue if the SSH key for the server you are connecting from is configured incorrectly or does not exist at all.
- [web@server git-temp]$ git clone firstname.lastname@example.org:user/project.git
- Initialized empty Git repository in /home/web/gittemp/.git/
- Permission denied (publickey).
- fatal: The remote end hung up unexpectedly
- fetch-pack from 'email@example.com:user/project.git' failed.
- [web@server git-temp]$
So configure a public SSH key on your server and then import it into github by following the instructions here.