my guess is that you don't have a value in the length, width or height cart columns.
try changing this code:
$Shipping_PackageArray[$Shipping_PackageIndex]["PackageLength"] = "".$eCart3->DisplayInfo("Length") ."";
$Shipping_PackageArray[$Shipping_PackageIndex]["PackageWidth"] = "".$eCart3->DisplayInfo("Width") ."";
$Shipping_PackageArray[$Shipping_PackageIndex]["PackageHeight"] = "".$eCart3->DisplayInfo("Height") ."";
to:
$Shipping_PackageArray[$Shipping_PackageIndex]["PackageLength"] = "12";
$Shipping_PackageArray[$Shipping_PackageIndex]["PackageWidth"] = "12";
$Shipping_PackageArray[$Shipping_PackageIndex]["PackageHeight"] = "12";