After applying cumulative 4 for Service Desk Manager 14.1, the export file extension has changed from xls to xlsx. When the export is created the format is not exported in a way that matches the content type, thus Microsoft Excel will refuse to open the file.
Service Desk Manager 14.1.04
To resolve you must apply the post Cumulative 4 patch that is currently located here:
This fix will be included in a future cumulative patch, thus this problem will only be present after applying Cumulative 4.