Hi sylviabyc,
Thanks for posting and welcome to the Community Forum.
I acknowledge how important importing is for your business. In my understanding, this error is likely caused by date formatting. It's possible that the formatting in your computer is not matched with the format in your file. It's best to export and import using the same computer. Also, if you are using Excel to edit your import files. You can check if it's in the correct format before exporting.
Don't hesitate to attach any screenshots or import material here if you require any further assistance.
Thanks,
Genreve