If you receiving "invalid data" errors when importing a contact list, here are some common reasons why and how you can fix them.  

Your spreadsheet is in Excel's XLS format when it should be in CSV format.

To fix this, be sure to always import CSV files. When using Excel, you can choose Save As to save your file in a CSV format (Fig 1).

Fig 1

Email addresses have trailing spaces and/or special (hidden) characters

To fix this, simply remove the trailing spaces.

The last column of the CSV formatted spreadsheet has some empty cells. Pinpointe is getting caught up on if records that have an empty cell in the last column are incomplete or if they are actual errors.

If there are any empty cells in your last column, reorder the columns to make sure the last column does not have any empty cells. For example, you could take the column that includes email addresses and move it over to the last column.  

After fixing these problems, try reimporting your list!