can't add contacts

can't add contacts

I have tried importing contacts from a file, but it doesn't work. My file has just 3 fields:
first name,last name,email address

When I put that header at the top of the file it won't import. I have tried .csv .xls and .xlsx. None worked.

What exactly should the header be in order for this to work. I have also tried selecting fields in the map fields page, but that didn't work either.