Hi there, Hoppers!
This can either be caused by a wrong API key, or the exchange's API server is temporarily not allowing your API to connect. This is often caused by an overloaded API server receiving too many requests. If this error is sporadic, it's nothing to worry about. If you're constantly seeing this error, you should generate new API keys.
Note: Some browsers (Most notably safari) Fill out the API key fields with the password for the website automatically. If you then save your configuration, this could be causing the issue.