ssh key duplicates

[dibus2]

Someone has already added that key as an access key to a repository.

[Nic Brough -Adaptavist-]

This means what it says - you've added an access key to a repository with another account.  

You should not be sharing keys between accounts, it's insecure, and Bitbucket explicitly does not allow it.

You will either need to log in with the old account and delete the key, or, better, generate a new key for the new account.