I've tried re-uploading those files again (I even deleted the ones I've uploaded already first)
I've tried uninstalling and re-installing the add-on that I think it is (email alerts)
I've re-downloaded the add-on from the Resource Manager and re-uploaded all of the files again.
Yet I'm still getting this error.
Any ideas what the problem may be? Is this of serious concern? Is this something that I should be contacting @Waindigo about, or a more general issue?