Have you had issues prior with other spreadsheets or was it just this particular one?
Are you creating a new table from the spreadsheet I am assuming
at least some of the issues I ran into was
making sure my header row had no spaces in it for the header columns. Phone Number 1 should be formatted as Phone_Number_1 and so forth
making sure the proper worksheet within the workbook is selected upon import. If your workbook has data located on multiple worksheets -which worksheet will you be importing data from?
Also if you are creating a new table for Contact List X -- make sure Contact List X is not being referenced by any other dialer campaign or script otherwise you will get a invalid data error.
not sure if any of this helps - hopefully it does