Try reinstalling Blockland.
My only other idea is that it's a client-side add-on. Try removing all add-ons that start with Client_ in C:\Blockland\Add-ons.
Have none of them
use page down? or you can get rid of it completely for viewing by setting max chatlines to 0, or setting the chat speed to 0, which will enable you to scroll up or down to view it (for the last option)