I got this error while doing an import into Magento:
Skipping import row, required field "sku" is not defined.
When I checked, all the rows did have a valid value for the SKU.
But, I had a few column names which contained special characters like this - text_with_specialÂcharacter.
When I changed the column names to something like text_with_special_character, and removed the special characters, the error went away and the import was successful.