This error message indicates an incorrectly configured category mapping in the catalogue.
For the categories, values should not be maintained side by side, but if necessary, stored as a fallback (alternative field, below the first field).

If it looks like this, please correct it: (otherwise the category value is transmitted twice)
 

It should then look like this: (then the category "Outdoor lights" only applies if "LED Outdoor lights" is not maintained on the item)