Error adding (TLS) certificate
This message occurs with TLS netstream driver. For TLS, certificates (.pem files) are needed to provide security credentials. This error is issued if there is a problem with these files. The message contains a more precise error description. That error text is taken directly from the underlying TLS library.
A common cause is that the file can not be found or accessed (permissions!). In that case, a rsyslogd-2040 error will follow.