The first thing you should do here is to close all programs that are using the Excel file you are attempting to open. Please ensure the .xls file is not opened in other workbooks, add-ins, or apps.

A file with the XLSX file extension is a Microsoft Excel Open XML Format Spreadsheet file. It's a ZIP-compressed, XML-based spreadsheet file created by Microsoft Excel version 2007 and later.

Open Microsoft Excel.; Go to “File > Options > Trust Center.” Now, click on the Trust Center Settings button.; Select Protected View from the left side.; Uncheck all the options on the right ...

XLS files are Excel workbook files created in Excel 97 or Excel 2003. The 2007, 2010 and 2013 versions of the program use the XLSX format by default to save workbooks, but can also use the XLS format.

If Microsoft Excel fails to recognize a file in the XLSX or XLS format, the data contained in the file could be corrupted. When you open a corrupted workbook in Excel, the program.