I've got a WinGrid of data.  The scrollbar on the right works fine when the rectangle on the scrollbar (i don't even know if it has a name) is clicked and dragged up and down.  But if I try to navigate using the up or down arrows of the scrollbar, or by clicking in between said rectangle and an arrow (which should page up or down in the grid), I get an error.

This does not occur in other grids I'm using.  The only differences are that I've added a couple of unbound columns to the grid.

Would someone please offer some idea?  I'm hoping it's a known problem with an easy fix, though I am all up to date with updates from Infragistics.  Thanks.