We have also replied to you via e-mail, but here is the reply for the benefit of the community:
If a public reply fails to send, and you receive a red system note in your ticket, then you can check the history entry for that note in the History tab of the ticket. It will have a resend button available. If there is no red system note nor a resend button available, it signifies that the note was successfully processed by the Lansweeper service. In those cases, we recommend that you simply copy/paste the failed note in a new note, add the attachments again, and try to send it out.