Item UPC is not a valid. A UPC must be 11 to 14 digits.
This is a Lightspeed limitation for the UPC field that we have guarded against.
If you have received this message when trying to import a file using Datatools it means that at least one line of the UPC column contains a UPC that is not 11 to 14 digits.
If you remove the data from these fields and are sure that "Do Not Update Blank Fields" is turned on as recommended, the UPC issue will be resolved.
If the UPC value is needed for Datatools matching purposes, it will need to be manually modified so that the UPC is 11 to 14 digits in Lightspeed, and in the spreadsheet.