Using Fire Bug to analyze the page, the content div is inside the left column div.
the content div should not be nested inside the left column div.
I seem recall you had a similar problem in another site before that ended up being caused by one of the 3rd part script libraries you had added. I had noticed a similar nesting problem, but when you inspected the pages code, the content div was not nested, not sure.
But at any rate, the content div being nested in the left column div is the cause of the problem.