This short article is repointing to http://blogs.technet.com/b/brenclarke/archive/2009/05/19/the-specified-file-is-not-a-valid-spreadsheet-or-contains-no-data-to-import-error-in-importing-a-excel-spreadsheet-in-bpos.aspx with image captured from the Internet Explorer 11. In the article on the previous URL, it was IE 8 and posted 2009. Somehow Microsoft does not change the error message for better understanding the problem.
When you add an app in Office 365 SharePoint Online, choose Import Spreadsheet then you receive an error “The specified file is not a valid spreadsheet or contains no data to import”.
Then you check you Excel file over and over again like me but there is nothing wrong with the Excel file. So I added the site into IE 11 as mentioned in the link above.
To add the link to IE 11.
1. Click Tools -> Internet Options.
2. Click Security -> click sites -> and add the URL