Excel Service can not display workbooks in Sharepoint 2010

Hi Everybody,

I have recently faced for a strange issue about displaying excel workbooks on Sharepoint 2010 .
When i checked the uls logs we have multiple exceptions like.

Stack trace: onetutil.dll: (unresolved symbol, module offset=00000000000A1A7D)
at 0x000007FEEFD71A7D onetutil.dll: (unresolved symbol, module offset=00000000000A2C3D)
at 0x000007FEEFD72C3D owssvr.dll: (unresolved symbol, module offset=0000000000008FA2)
at 0x000007FEE9A58FA2 owssvr.dll: (unresolved symbol, module offset=0000000000048C74)
at 0x000007FEE9A98C74 mscorwks.dll: (unresolved symbol, module offset=00000000002BF6D7)
at 0x000007FEF365F6D7 Microsoft.SharePoint.Library.ni.dll: (unresolved symbol, module offset=00000000000EC86B)
at 0x000007FEEB45C86B Microsoft.SharePoint.ni.dll: (unresolved symbol, module offset=0000000001AB6942)
at 0x000007FEED476942 Microsoft.SharePoint.ni.dll: (unresolved symbol, module offset=0000000001A7ADED)
at 0x000007FEED43ADED Microsoft.SharePoint.ni.dll: (unresolved symbol, module offset=0000000001A7CF66)
at 0x000007FEED43CF66 Microsoft.SharePoint.ni.dll: (unresolved symbol, module offset=0000000001A7FA31)
at 0x000007FEED43FA31

An internal error occurred.
at Microsoft.Office.Excel.WebUI.ExcelWebRendererControl.InternalPreRender()
at Microsoft.Office.Excel.WebUI.Utils.ExecuteWebEventHandler(CoreWebEventHandler coreWebEventHandler, CoreWebEventHandler baseClassHandler, Object param, IMainControl mainControl)

Utils.ExecuteWebEventHandler: unexpected exception System.NullReferenceException: Object reference not set to an instance of an object.
at Microsoft.Office.Excel.WebUI.ExcelWebRendererControl.InternalPreRender()
at Microsoft.Office.Excel.WebUI.Utils.ExecuteWebEventHandler(CoreWebEventHandler coreWebEventHandler, CoreWebEventHandler baseClassHandler, Object param, IMainControl mainControl)

Watson bucket parameters: SharePoint Server 2010, ULSException14, 5f9be61a “excel services application”, 0e00178d “14.0.6029.0”, 13ed43ce “microsoft.office.excel.webui.internal”, 0e00178b “14.0.6027.0”, 4da5bd73 “wed apr 13 18:12:51 2011”, 000009ca “000009ca”, 000000e9 “000000e9”, 4a6d3421 “nullreferenceexception”, 62646b69 “bdki”
The file that i want to open have url like http://blog.bugrapostaci.com:80/_layouts/xlviewer.aspx?id=/Shared%20Documents/CaseTest.xsls…
But  the important one is in logs   in this correlation that unrelated information log not the exceptions. This info is about :
“There is no Web named “/SiteDirectory/BlogContent/Lists/Categories/AllCategories.aspx”. in first i ignored it quickly. Than i realized that article:

Excel Calculation Service cannot display workbooks if no root site collection is created for a web application.
http://support.microsoft.com/kb/2596582

The sharepoint version which i was working on it is before Oct 2011 CU . The Solution is simple install at least Oct 2011 CU for fixing these errors.