An error was detected by the partner IdP and it's reporting it to the SP by sending an error status SAML response. Usually, for security reasons, the error status is very generic (eg Responder).
The most likely cause is some sort of configuration mismatch between the IdP and SP.
Please check your local SAML configuration to ensure it looks correct.
If there's still an error, you'll need the IdP to check their logs for the exact cause of the issue.