If you are getting permission denied when working with git on a remote server using a key, this may help.
First test to ensure the key will be accepted by the remote server.
ssh -v firstname.lastname@example.org
Look for these lines in the output:
debug1: Next authentication method: publickey
debug1: Offering public key: /home/account/.ssh/example.key
debug1: Server accepts key: pkalg ssh-rsa blen 277
debug1: Authentication succeeded (publickey).
Then check your ~/.ssh/config file. Be sure the user is in the file and matches what worked with the ssh test.
Now get back to work.