When performing a scheduled report distribution of a report with the attachment type of Microsoft Excel, the attached file is using the old file extension of XLS rather than XLSX. This causes Excel to bring up a warning message when opening the file. Image description
The issue is related to a change over of Excel attachments in Archer 6.5+ to the new Excel format of .xlsx. Scheduled Report Distributions was skipped when updating the extension name.
This issue has been fixed in 6.5 Patch 3 and later.
Change the file extension to XLSX or select "Yes" on the popup to open the file.