There are a lot of questions about this error, but I even get it for a public git repo. I'm a little bit lost about how to track down the issue.
PS C:\dev> git clone git@github.com:golang/dep.git
Cloning into 'dep'...
git@github.com: Permission denied (publickey).
fatal: Could not read from remote repository.
Please make sure you have the correct access rights
and the repository exists.