PHP Warnings with custom-user-meta.php

Hey there,

I am seeing loads of PHP-Warnings like this firing:

[28-Apr-2015 06:37:31 UTC] PHP Warning:  include() [<a href='function.include'>function.include</a>]: Failed opening '/var/www/my-domain/htdocs/wp-content/plugins/cbnet-multi-author-comment-notification/custom-user-meta.php' for inclusion (include_path='.:/usr/share/php5:/usr/share/php') in /var/www/my-domain/htdocs/wp-content/plugins/cbnet-multi-author-comment-notification/cbnet-multi-author-comment-notification.php on line 56
[28-Apr-2015 06:37:35 UTC] PHP Warning:  include(/var/www/my-domain/htdocs/wp-content/plugins/cbnet-multi-author-comment-notification/custom-user-meta.php) [<a href='function.include'>function.include</a>]: failed to open stream: No such file or directory in /var/www/my-domain/htdocs/wp-content/plugins/cbnet-multi-author-comment-notification/cbnet-multi-author-comment-notification.php on line 56
[28-Apr-2015 06:37:35 UTC] PHP Warning:  include() [<a href='function.include'>function.include</a>]: Failed opening '/var/www/my-domain/htdocs/wp-content/plugins/cbnet-multi-author-comment-notification/custom-user-meta.php' for inclusion (include_path='.:/usr/share/php5:/usr/share/php') in /var/www/my-domain/htdocs/wp-content/plugins/cbnet-multi-author-comment-notification/cbnet-multi-author-comment-notification.php on line 56

Can you reproduce this? Anyone else seeing those? How to fix?

Thanks + regards,
Henning

https://wordpress.org/plugins/cbnet-multi-author-comment-notification/