Excel calculation services – The Workbook cannot be opened

Symptom:

When you configure the Excel calculation services (ECS) on your SharePoint2010 farm it might happen that you (or latest your endusers) face some error when trying to open an excel sheet stored in a document library.

When you check your ULS logs, you will find something like:

ServerSession.ProcessServerSessionException: An exception during ExecuteWebMethod has occurred for server: http://yourserver andsomeguid/ExcelService*.asmx, method: OpenWorkbook, ex: Microsoft.Office.Excel.Server.CalculationServer.Proxy.ServerSessionException: The workbook cannot be opened..

Result=Microsoft.Office.Excel.Server.CalculationServer.Proxy.ServerSession Exception: The workbook cannot be opened.  
at Microsoft.Office.Excel.Server.CalculationServer.Proxy.ServerSession.Execute WebMethodCore(WebMethodType webMethodType, WebMethodBehaviorAttribute webMethodBehavior, CommandParameter parameter, CoreWebMethod coreWebMethod)  
at Microsoft.Office.Excel.Server.CalculationServer.Proxy.ServerSession.Execute WebMethod(WebMethodType webMethodType, WebMethodBehaviorAttribute webMethodBehavior, CommandParameter parameter, CoreWebMethod coreWebMethod)

To solve this error, the account that is running the Excel Services application pool must have access to the content database where the PWA site resides.

To correct it, just run the script below:

$w = Get-SPWebApplication -identity “http://ourserver.domain”    # change here to the correct web application
$w.GrantAccessToProcessIdentity(“Domain\UserAccountThatRunTheExcelService”)

Ok, now all content databases hosted on this web application should have received dbowner role for that user account (Excel Service Account).