On a "Page" page (home page), I first removed the left side bar by entering page ID in "LEFT sidebar: Don't display on Pages: " of Atahualpa Theme Options/Side Bar section.
I now changed my mind and deleted the page ID to get it back, but can't get the left side bar back.
Also, I created the second "Page" page and expected to enter the page ID to remove the left side bar as well, but it showed up automatically without the left side bar. I now want the left side bar also on this page (and all future pages). What to do? Shall I delete everything and start from a scratch? Or would that confuse things?

1) Are all the boxes at ATO -> Sidebars -> Left Sidebar: Display on: checked?
2) is ATO -> Sidebars -> Left Sidebar: Don't display on Pages: blank?
3) is ATO -> Sidebars -> Left Sidebar: Don't display on Categories: blank?

Oh, 1) One of the critical boxes on "Page" pages was still unchecked! I put the check mark back on it, and it worked. Thank you!!!