Excel Web Access Error in Sharepoint 2007

I wanted to use Excel Services on Sharepoint 2007 to migrate some of our BI reports from a third party application that we use. So I tried publishing to Excel Services from Excel 2007 assuming that our Sharepoint was setup to be used with Excel Services.
When I tried to publish and open in a browser I started getting an error "Excel Web Access: An error has occurred ".
When I checked the event log the following was logged in the event viewer.

There was an error in communicating with Excel Calculation Services http://sharepoint:56737/SPAdmin/ExcelCalculationServer/ExcelService.asmx exception: The request failed with HTTP status 401: Unauthorized.
[Session: (null) User:[Domain\user].

I have followed all the following steps to get to this stage.

• I have created a document library
• Added this document library as a trusted file location
• Added the document library to trusted data connection libraries
• Also ensured that the user being used has the proper rights in each of the databases
• Started the single signon service
• Ensured that the Excel Calculation service is running

Still the error was persistent. After a lot of struggling for 3 days, I finally fixed the problem by removing the integrated windows authentication option on the ExcelCalculationServer folder from the Office Server Web Services website on IIS.