I have been getting this error every time I try to upload TeamRaiser gifts and I'm not sure what is wrong in the file.
This error occurs when the GIFT_DATE is entered with an invalid format. The format should be MM/DD/YYYY. The most common issue is that you're probably using 2 digits for the year instead of 4.
Tip: Check the format of your cells and make sure its using 4 digits for the year. If the dates are formatted to take in values such as dd/mm/yy, then even if you enter 4 digits for the year, it will revert back to 2 and it often goes unnoticed.