@GregorS
The problem is with your server. Notice the log lines
14.12.2015 12:53 Data::RSA ERROR: Certificate validation failed
14.12.2015 12:53 Data::RSA ERROR: Trust chain did not complete to the known authority anchor. Errors: The signature of the certificate cannot be verified. (NotSignatureValid)
14.12.2015 12:53 Middleware::Authentication ERROR: Could not authenticate
14.12.2015 12:53 Middleware::Authentication ERROR: Certificate is not from FOG CA
@Tom-Elliott would be able to help you debug why your server certs are incorrect.