The Open window appears on your screen. Make sure the "All Excel Files" option is selected in the drop-down box next to File Name. Excel may not display the XLS file if another option is selected ...

If you cannot open the Excel file from its location, simply open any Excel file and click the File tab. Then, go to Open > Browse and select the file giving error ...

In the past, XLS files ... would still open the workbook without Protected View security. After the security updates Excel no longer will open the workbook because these files are not compatible ...