The error message could be the result of several things. However, most likely its complaining that it doesn't recognize your SSH.
Can you double check that the key your client is using is the one associated with your account? You can determine that by issuing the following command "ssh -Tv git@bitbucket.org".
Check out our troubleshooting guide for more details:
https://confluence.atlassian.com/display/BITBUCKET/Troubleshoot+SSH+Issues
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