Fatal Error on StCR Auto-Importation

I receive this error every time I try to import subscribers from Subscribe to Comments Reloaded:

Fatal error: Uncaught Exception: Insert/replace failure. in /home/jessic06/public_html/wp-content/plugins/comment-mail/src/includes/classes/SubInserter.php:721 Stack trace: #0 /home/jessic06/public_html/wp-content/plugins/comment-mail/src/includes/classes/SubInserter.php(695): WebSharks\CommentMail\SubInserter->insert() #1 /home/jessic06/public_html/wp-content/plugins/comment-mail/src/includes/classes/SubInserter.php(479): WebSharks\CommentMail\SubInserter->maybeInsertUpdate() #2 /home/jessic06/public_html/wp-content/plugins/comment-mail/src/includes/classes/ImportStcr.php(254): WebSharks\CommentMail\SubInserter->__construct(Array) #3 /home/jessic06/public_html/wp-content/plugins/comment-mail/src/includes/classes/ImportStcr.php(178): WebSharks\CommentMail\ImportStcr->maybeImportSub(1824, Object(stdClass)) #4 /home/jessic06/public_html/wp-content/plugins/comment-mail/src/includes/classes/ImportStcr.php(139): WebSharks\CommentMail\ImportStcr->maybeImportPost(1824) #5 /home/jessic06/public_html/wp-content/plugins/comment-mai in /home/jessic06/public_html/wp-content/plugins/comment-mail/src/includes/classes/SubInserter.php on line 721