The error from UPS is:
"A shipment cannot have a KGS/IN or LBS/CM or OZS/CM as its unit of measurements"
so basically if you are setting your weight in KGS you need to set the width in CM not IN. You can just look on the confirm_cart page for this line:
$Shipping_PackageArray[$Shipping_PackageIndex]["SizeUnits"] = "IN";
and update it to:
$Shipping_PackageArray[$Shipping_PackageIndex]["SizeUnits"] = "CM";