In some scenarios, an Excel Web Access web part won’t display an Excel workbook that will display correctly with Excel Services (xlviewer). Instead of seeing the published workbook contents in the web part, there is just a placeholder icon where the workbook should be displayed, and there are no errors in the web part or on the page.
In this scenario, if you look at the Internet Explorer Developer Tools (IE > Tools > Developer Tools) while you attempt to display an Excel workbook in an Excel Web Access web part, you may see errors like this one “TypeError: o.getName is not a function”.
We have seen this issue with at least these versions of SharePoint 2013:
This can be caused by an issue with compatibility between the .NET AJAX Control Toolkit and the Excel Web Access web part.
Do not use the .NET AJAX Control Toolkit to implement Ajax functionality for a site using Excel Web Access web parts.