The path that you are using is not invalid "1/2/16"
What giving you the error is the wrong ID of category. Make sure all the IDs in path are valid category IDs.
In magento 1.9, mostly category path starts with 2 Since 2 is the default category ID.
One more thing to ensure: Last ID of path should be equal to the name of the category. Like ID 16 name should be equal to the name in csv
You need to dubug
function getCategoryIdFromPath() in file
This is the function responsible for the error that you are facing.
If this function returns empty array then error will appear