error/block moodletxt/errornopermissionmessage
From MoodleDocs
Attempting to Access a Message You Do Not Have Permission to View
You have attempted to view the details of a sent message within MoodleTxt, and received the following message:
You are not authorised to view this message.
Cause
The message you have attempted to view does not belong to you, and you do not have the necessary access level to view another user's message details.