You cannot change the 'item_classification' for SKU

You cannot change the 'item_classification' for SKU 'test-pants-s' by submitting a feed with a new value. To change this attribute, do the following: 1) Submit a feed to delete the existing SKU. 2) Submit a feed to recreate the SKU with the updated 'item_classification'.

This error appears when you are trying to provide a new classification value for the product that has already been added to your Seller Central account. 

Every marketplace has its own classification system. Make sure to match the existing classification when you submit a new Amazon listing.