Hi Aaron,
The error message from Amazon is : "AMAZON : AWS was not able to validate the provided access credentials". We assume that you changed your AWS credentials from AWS console. In this way CAL account is going to be invalid and cannot operate with the instance in Amazon. In other hand CAL has protection of changing account credentials if you have running instances due to keep consistency. Could you please check in Amazon and confirm that this instance is not available there. If it is so please let us know and we'll do the manual clean up.
Best Regards
Stela