Submissions go to DB but can't be emailed.

Hello there,

After installing the Simplenews and Mime modules for D7, I have been getting the following error when any sort of mail action is attempted on my website.

Warning: class_implements() [function.class-implements]: object or string expected in drupal_mail_system() (line 247 of /services4/webpages/util/p/e/peruschallenge.site.aplus.net/public/includes/mail.inc).
Exception: Class does not implement interface MailSystemInterface in drupal_mail_system() (line 252 of /services4/webpages/util/p/e/peruschallenge.site.aplus.net/public/includes/mail.inc).

I disabled and tried to uninstall those modules, but for some reason they didn't uninstall correctly and the error remains.

The forms were previously working fine. Any help is greatly appreciated.

Jonathan