Original post by: E Stinson ,
From past experience with touchscreen interactive whiteboards, there is problem a sensor that is sticking in that corner. The manufacturer's tech support directed us to take the flat of our hand and run it over the screen to try to un-stick the possibly stuff sensor. This usually did the trick and is common especially if that spot is used often or was pressed in harder than normal for some reason. I suggest running your hand over the entire screen and not just that corner. I hope this helps.