Sometime you receive error message “Unable to process the request” as picture below:
If open the Event Viewer in SharePoint Server, you will se the exactly error message related to Excel Services as below:
There was an error in communicating with Excel Calculation Services http://SPSERVER2:32843/1d6c7449da5d4abd9e3e12d23d550738/ExcelService*.asmx exception: An error has occurred.
In this case, the workaround is restart IIS by open CMD as Administrator mode then run the IISRESET commands.
Hope this help!