This error occurs when a user is missing either Item or Supplier Keys when attempting to Import via a CSV upload. This is easily remedied by either creating your own Item or Supplier Key for existing items and inputting the correct Item and Supplier Keys shown when you downloaded the existing data.
If you get an Import Errors message:
This could mean the same as above, a primary key is missing. It also could mean you are missing an item/supplier name, or you entered data that does not match previously entered information.
For example, if you are in the "items" tab trying to add a new item and the supplier name entered with it does not exist in the "Suppliers" tab already, the system will not be able to pair that item to its supplier until you go back to "Suppliers" and add it in.
The error message will tell you which lines of your CSV file need attention.