I've been trying to add a private key for a while now using SourceTree and OpenSSH. I have tried all the solutions and derivations proposed in this answer to no avail. I've tried all variations of
eval `ssh-agent -s`
ssh-add
that I've found. I disabled all firewalls, antivirus, and even tried it in netorked safe mode. The first command runs fine, and the agent gets a pid, but the ssh-add command throws the error in the title every time. I've also used different names for the .pem file, including the original name and location, username/.ssh/id_rsa.pem (some people had had problems due to the file name), etc., but nothing changes.
I can connect manually to the repository by using the command
ssh -i /route/to/key/key_name.pem ubuntu@serverip
but I want to be able to use it to push changes to the repo through Git. I'm really stumped on this one, and I'm by no means an expert. Can anyone think of another reason for this?
In the end I had to give up on using OpenSSH for Windows. I installed PuTTY, transformed the .pem key into a .ppk with PuTTYgen, and added the private key with SourceTree without trouble.