Blank Installation of Project Server 2010 with SP1 - Excel Services not working

Today faced problem described in several other blogs about problem with Excel Services not working when you upgrade Project Server 2010 to SP1 (exisiting or new).

The reason for the error is if there is no root site collection in "yourdomain/" (that was my case, I created just PWA) Excel services in not working and giving the JavaScript error starting with  "http://<your_domain>/_layouts/EwaStringsHandler.ashx/en-US?......."

To resolve - go to Central Administration and create blank site collection at the root of your SharePoint Server and refresh the excel report - it will start working immediately.