A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data
The message suggests a problem with an add-in for Excel.
Template add-ins would usually be in the XLStart folder which you can access via the Run dialog box. Hold the Windows logo key as you press R; in the Open dialog box, type %appdata%\Microsoft\Excel\XLStart and press Enter.
With Excel closed, move any macro-enabled files out of that folder and see if the error message goes away.