What is that div, why does it exist, does it have an ID on it or a parent with an ID on it?
It might even be a completely unnecessary div as the behavior may be better placed on all those div being closed above it (though really closing 4 div at once usually means excess/unnecessary div in the layout in the first place!) -- but without seeing the CONTENT being plugged into the code, anything we tell you is guessing wildly.
Remember, semantic markup with meaningful names on the elements FIRST, THEN worry about layout and CSS; this is where the majority of coders who thought HTML 3.2 was the be-all end-all and still vomit it up today with a tranny doctype on it really tend to drop the ball.
If it's the page you pointed to on my visitor page, then it's DEFINATELY an unneccessary element as that's not even applying clearfix correctly, and is instead treating it like the old clearing DIV -- at which point all .clearfix needs to be is "clear:both" and forget the rest.
<div id="colmid"><div id="colleft"><div id="col1wrap"><div id="col1">
being pointless wasteful and for the most part presentational markup. Has no place on the page... see the rewrite I did for you that did away with that and while it has almost as many DIV, those DIV have meaningful names saying what things are on them, and doesn't need that clearfix nonsense as #columnWrapper is handling that. (with width:100% and overflow:hidden;)
You did get that link for the rewrite via PM, right?
Where you have:
My rewrite has:
<!-- #secondSideBar --></div>
<!-- #columnWrapper, #pageWrapper --></div></div>
Two less div and no clearfix nonsense needed... and comments to tell you what's being closed.