I have had similar issues before with CSV, even though everything looks good. If you are on a PC, try downloading Notepad++ and then open the csv file in there and view it.
Depending on how the data was inputted into the csv or where they were acquired from, sometimes hidden invalid characters show up.
If that shows nothing, try opening in notepad or ++ and convert to plain text, then reimport back into excel and create a new .csv.
Hope this solves your issue.