2301027 - Warning message when opening Ad Hoc XLS Export File stating the format and extension of Report don't match

For any report in any instance try to export to excel (xls) and the pop up appears. If you click on open the following message is shown:
The file format and extension of 'report_XYZ_...........xls' don't match. The file could be corrupted or unsafe. Unless you trust its source, don't open it. Do you want to open it anyway?

SAP SuccessFactors HCM Core

1. Login to the instance
2. Analytics - Reporting - Ad Hoc
3. Select run then export to excel (xls) click on open an the below is shown:
   The file format and extension of 'report_XYZ_...........xls' don't match. The file could be corrupted or unsafe. Unless you trust its source, don't open it. Do you want to open it anyway?

Note:

• If you save the file locally and then open it the warning message doesn't occurr.
• With CSV download or PDF export the pop up doesn't occur.

The report behaviour is as designed.

The issue can be resolved by enabling the following switch in provisioning:
Company Settings >
'Generate Excel 2010 Output for Adhoc Reports'
This will generate the report(s) in xlsx format.

If this doesn't fix the issue, the report behaviour is as designed and unfortunately we cannot change anything with this behaviour.
 
If you click on yes the data is correctly shown.
Additionally, if you save the file locally and then open it the warning message doesn't occur.
 
Further information on the 'warning message' may also be available via the following link/site:
Excel 2007 Extension Warning On Opening Excel Workbook from a Web Site
Link: https://blogs.msdn.microsoft.com/vsofficedeveloper/2008/03/11/excel-2007-extension-warning-on-opening-excel-workbook-from-a-web-site-2/

excel export error, error opening excel , KBA , LOD-SF-ANA-ADH , Adhoc Reports & Report Builder , Problem