A GitHub account can only be connected to one Glitch account.

This error typically occurs if the GitHub account that you are trying to connect to is already linked to another Glitch account.    

You can fix this by:

1. Closing the other glitch account that is currently connected to the GitHub account.
2. Clearing your browser cache.
3. Then, login to your newer account and retry your action.

If you need help figuring out what Glitch account is currently connected to your GitHub account, please contact Glitch Support and let us know what email is associated with your GitHub account.