You likely have some cells merged across the two. If you try to select the entire column, it has to also select that cell, and to be consistent, it then has to select the rest of the cells that line up with it (i.e. column G). Scan visually down the columns and look for a cell that spans both. You can either delete the row containing that cell, or split it into columns (don't recall which menu, though you can right-click and do it from there).
jW