image not displaying in grid, just text

I'm trying to put an image in a cell, but it never appears.... i just get the text of the data value:

I have:
.aw-image-logout {background:url(/images/icons/logout.gif) no-repeat;}

and the last column for every row in my data array is ...,"logout"]
then i have:
obj.setCellTemplate(new AW.Templates.Image, 8);
obj.setCellImage(myData);

can anyone tell me why the image is not being displayed? The last column in every row just contains the string value "logout"