REU, I've also had that trouble, it seemed to happen randomly for me. You should see a little arrow in the middle of the border of the column, they should be on the right, left and center columns. Here's a screenshot: http://screencast.com/t/30FW7NRtX. Look just to the left of where it says "Private Author Notes"
Click that, its a button. then try mousing over the border and see if you get the icon to expand it, then simple click and drag. Hope that helps.