6f21ed28_int_2013___My_SharePoint_Space__Description
[Feature] Excel Services — Can’t edit workbooks in the browser that have external data connections [Reason] This is a design limitation in SharePoint 2013. [Description] 
Workbooks with external data connections that use Windows authentication cannot be refreshed in the browser. Instead, you are prompted to open the workbook in the Excel client program.
Deprecated Features in SharePoint 2013 | My SharePoint Space
Description