As of right now there's no option to do it in bulk. I might take a look at it to implement it in a future release. For now, you'd have to do it manually. I am sorry for the inconvenience and as soon as it is implemented I'll let you know.
When you say the attachment permission error, do you mean you have it set to No and the addon is allowing those users to upload files anyways? Or is it the other way around?
They only appear like this because the addon effectively hides the attachment management option from users without the permission to delete them. The alternative is to keep the attachment management section, but then they will see the "Attach files" button, and will be able to delete the [bbcode] tags from the message area. However, you can easily recover those from the edit history.
