As the author you can remove messages from the chat if you want to. We allow this since it is your ePoster and so you should have control over what is posted in the chat area and should be able to remove something if you don't want it there.
Only the editing author and the domain administrator can remove messages from an ePoster's chat area.
To remove a chat message, first view your ePoster and open its chat area. Next to each message you will see there is a small edit icon. Click on the edit icon and you will then see a small bin icon appear in the message. If you click on the bin icon then that message will be deleted (see annotated screenshot below).