Sorry, but to open this workbook, your computer must be running a supported version of Microsoft Excel
Since installing Office 365 ProPlus (I was originally using Office 2016 ProPlus but now have an Office 365 account) on my desktop computer any documents I open in SharePoint 2013 open in Office Web Apps despite the document library being set to open in the client application. Then, when trying to edit the document, a get this message:
Sorry, but to open this workbook, your computer must be running a supported version of Microsoft Excel and a browser that supports opening files directly from Office Web Apps.
After some investigation I noticed that there are multiple versions of Office installed (EN-US and CY-GB) so I removed the Welsh version and the problem went away!