I guess this is due to the removal of several language files from the /installation directory that happened today (they're probably packing rc4 and these translation teams are late... too bad).
* JInstaller::install: The language file 'www/language/da-DK/da-DK.com_yvcomment.ini' could not be installed because the Administrator language package for 'da-DK' has not been installed or does not exist.
* JInstaller::install: The language file 'www/language/de-DE/de-DE.com_yvcomment.ini' could not be installed because the Administrator language package for 'de-DE' has not been installed or does not exist.
* JInstaller::install: The language file 'www/language/es-ES/es-ES.com_yvcomment.ini' could not be installed because the Administrator language package for 'es-ES' has not been installed or does not exist.
* JInstaller::install: The language file 'www/language/fa-IR/fa-IR.com_yvcomment.ini' could not be installed because the Administrator language package for 'fa-IR' has not been installed or does not exist.
* JInstaller::install: The language file 'www/language/nl-NL/nl-NL.com_yvcomment.ini' could not be installed because the Administrator language package for 'nl-NL' has not been installed or does not exist.
* JInstaller::install: The language file 'www/language/ru-RU/ru-RU.com_yvcomment.ini' could not be installed because the Administrator language package for 'ru-RU' has not been installed or does not exist.
* JInstaller::install: The language file 'www/language/sv-SE/sv-SE.com_yvcomment.ini' could not be installed because the Administrator language package for 'sv-SE' has not been installed or does not exist.
* JInstaller::install: The language file 'www/language/tr-TR/tr-TR.com_yvcomment.ini' could not be installed because the Administrator language package for 'tr-TR' has not been installed or does not exist.
* JInstaller::install: The language file 'www/administrator/language/de-DE/de-DE.com_yvcomment.ini' could not be installed because the Administrator language package for 'de-DE' has not been installed or does not exist.
* JInstaller::install: The language file 'www/administrator/language/es-ES/es-ES.com_yvcomment.ini' could not be installed because the Administrator language package for 'es-ES' has not been installed or does not exist.
* JInstaller::install: The language file 'www/administrator/language/fa-IR/fa-IR.com_yvcomment.ini' could not be installed because the Administrator language package for 'fa-IR' has not been installed or does not exist.
* JInstaller::install: The language file 'www/administrator/language/nl-NL/nl-NL.com_yvcomment.ini' could not be installed because the Administrator language package for 'nl-NL' has not been installed or does not exist.
* JInstaller::install: The language file 'www/administrator/language/ru-RU/ru-RU.com_yvcomment.ini' could not be installed because the Administrator language package for 'ru-RU' has not been installed or does not exist.
* JInstaller::install: The language file 'www/administrator/language/sv-SE/sv-SE.com_yvcomment.ini' could not be installed because the Administrator language package for 'sv-SE' has not been installed or does not exist.
* JInstaller::install: The language file 'www/administrator/language/tr-TR/tr-TR.com_yvcomment.ini' could not be installed because the Administrator language package for 'tr-TR' has not been installed or does not exist.
Despite these errors, the component seems to be working well. (thanks for adding the mail notification feature yuri!)