Due to a technical error, a non-final version of Newsletter 4.7 has beeen released: if you are experiencing any issues, please reinstall version 4.7 through the WordPress repository.
Regards,
Roberto
Hi, those kind of error are logged by the server in a special log file, named error.log. Ask the provider this file and check if your php version (on newsletter diagnostic panel) is 5.3 or greater.