requests for grid.png

My activewidjets JS include is in a certain folder, say /x/y/z. In looking at my http error log, I see a bunch of failed requests for "x/y/z/grid.png". I am at a loss as to where this request is initiated. Do you have any ideas? THanks.

This request is probably coming from CSS
in css/activeui/classic/box.css there exists

.active-sort-ascending .active-box-sort {
width: 16px;
background: url(grid.png) -20px 50% no-repeat;
}

.active-sort-descending .active-box-sort {
width: 16px;
background: url(grid.png) -40px 50% no-repeat;
}


which I believe gives the up/down arrows for the grid column sort direction indicators.