If an Excel workbook in XML Spreadsheet format (*.xml) is stored as a UTF-16 Unicode text stream, you may have problems opening it in the expected program when trying to open it through Windows Explorer or Windows Internet Explorer. This problem can occur if you have Office 2013 or an Office 2013 component installed.
You have an Excel file that was created by Dynamics CRM. When double clicking on it in Windows Explorer, the file may try to open in Notepad or Windows Internet Explorer, rather than Excel 2013.
Install the hotfix below.
Hotfix KB2883063 for Office 2013 September 9, 2014 (Xmleditverbhandler-x-none.msp)