Locate an Excel file you would like to display in Excel Web Access. For this example, the Excel file is called, stoplight.xlsx. It is stored in a document library at http://sample1portal.domain.com/excelfiles_site/excelfiles_library/
Verify that the intended audience has permission to view the file.
Verify that Excel File location is trusted by Excel Services.
If you have not done so previously, run the following command:
Add the Excel Web Access web part to a page to display stoplight.xslx. Since you have enabled cross domain access, it will now display regardless if the Excel file is part of the same web application as the Excel file, or in a different web application.
In this example, I am displaying the Excel Web Access Web Part on a sub site of http://sample2portal.domain.com although the Excel file is being stored on http://sample1portal.domain.com.