Open Excel file in browser returns error

I have configured an excel document library to open in the browser.

The file was published to the document library.

The document library was set to open the file in the browser.

When the file is clicked, it makes an attempt to open the file in the browser but it returns an error message.

Unable to process the request.

Wait a few minutes and try performing this operation again.

What else is necessary to get the Excel file to open in the browser?