Please ensure that you're checking in ACP -> Members -> Groups -> edit Guest -> Can access site?
If that is enabled, we would need to investigate further.
We would need to look further into this for you, however the access details on file appear to be incorrect or missing. Could you please update these details by visiting your client area, selecting the relevant purchase, then clicking "Review/Update Access Information" under the "Stored Access Information" section.
We look forward to further assisting you.