If you receive an error downloading a report from Sharepoint, the likely cause of this is because the file type is in an incompatible format.
To make sure your file is uploaded in the correct format, Save As and in the drop-down option, select .xls not .xlsx
.xls is Excel 97-2003 Workbook format. If you save to 'Excel Workbook' it will be the .xlsx format that isn't compatible.
Uploading the file in the correct format prevents users from having download issues.