I have followed the process described in Multiple GitHub Accounts & SSH Config (stefano's answer) and have set up SSH access to multiple repositories using deploy keys. I've tried that on repositories of a specific GitHub organization and it works fine - I can pull and push changes. I've also tried this on my user area and it still works great.
However, when trying this on repositories in another GitHub organization (e.g. when doing a git push) it fails with the following error
ERROR: Permission to XXXX/YYYY.git denied to deploy key
fatal: Could not read from remote repository.
Please make sure you have the correct access rights
When checking SSH access through ssh -T
I get
"Hi XXX/YYYY! You've successfully authenticated, but GitHub does not provide shell access."
which suggests that SSH should be working.
I have gone through the organization settings (main page for GitHub organization > Settings) and they have pretty much identical settings, except from what you would expect to be different e.g. contact email etc.
I was wondering if anyone has any ideas about what could be causing this. Are there any more organization settings somewhere by any chance?