updates not being matches

Hi,
I have a file with each entry containing:
sku, case material, width, length, thickness, diameter, special

I want to just update. Not create any new items. How does all import match existing posts to the fields I am entering? I tried setting automatic matching using {sku} but this does not work. It does not find any matches. How do I tell All import to match the post title of existing products to the sku field in my file?

http://wordpress.org/extend/plugins/woocommerce-xml-csv-product-import/