service fail to save file to hard drive on windows server 2008

I have a windows service that will get data from database and create excel spreadsheet on hard drive. now this service is required to run on windows server 2008, however, it failed when call saveas method. the error is "System.Runtime.InteropServices.COMException (0x800A03EC): Exception from HRESULT: 0x800A03EC"
However, I also have a test windows form app which use exactly same code, and I can run that app successfully on windows server 2008, create/read the spreadsheet just fine.
I'm wondering if there's some new restriction for windows service? how can i remove the restriction so my service can save the file.
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Setup a user and run the service with this account.  Make sure the account has rights on the folder where the spreadsheet is being saved and on the file itself.  
dragonempAuthor Commented:
it's not folder permission problem since I have given everyone full control on the folder for testing purpose.....
it has something to do with the way windows server 2008 handles service/DCOM, because that's the only difference between my test app and the service itself.
Have you done this
Enabling DCOM in Windows Server 2008
In order to make DCOM applications work in Windows Server 2008 you need to do two things. Installing the Application role is not needed (but it does add the COM+ network access as in 1) below).

Allow "COM+ network access" in firewall rules (type firewall.cpl from a command prompt and on the left you'll see the setting). COM+ is somewhat of a The out-of-box configuration for Windows Server 2008 the Network Access Protection Agent start-mode is manual. Once I changed the start mode for that service and restarted the server the DCOM error was corrected.since it is also for DCOM. COM+ Network Access is a preconfigured program in the exception list that you can just check off.
Add your DCOM server to the list of program exceptions in the firewall

Check permissions in

The out-of-box configuration for Windows Server 2008 the Network Access Protection Agent start-mode is manual. Change the start mode for this service and restart the server.
Making Bulk Changes to Active Directory

Watch this video to see how easy it is to make mass changes to Active Directory from an external text file without using complicated scripts.

dragonempAuthor Commented:
I disabled windows firewall from begining so that's not the issue.
and I already have application server role installed.
for the network access protection agent service, I fail to see the relationship of this and the issue, but I started it anyway, still no luck.
Can you post you code that produces the ss
dragonempAuthor Commented:
remember: same code works on a windows form app, so it must have something to do with service/DCOM permission
string xPath = "/root/" + templateName.Replace(" ","") ;
				XmlNode templateTypeNode = xmlDoc.SelectSingleNode(xPath) ;
				excelApp = new Excel.ApplicationClass() ;
				excelApp.Visible = true ;
				excelApp.AutomationSecurity = Microsoft.Office.Core.MsoAutomationSecurity.msoAutomationSecurityForceDisable ;
				//Creating Excel workbooks and worksheets
				_workBook = (Excel.Workbook)(excelApp.Workbooks.Add(missing)) ;
				_workSheet = (Excel.Worksheet)_workBook.ActiveSheet ;
				_workSheet.Name = templateName.Replace (" ", "") ;
				ValidationDataWorkSheet = (Excel.Worksheet)(_workBook.Worksheets[2]) ;
				ListRelationsWorkSheet = (Excel.Worksheet)(_workBook.Worksheets[3]) ;
				ValidationDataWorkSheet.Name = "Validation Data" ;
				ListRelationsWorkSheet.Name = "Validation List Relations" ;
				//Getting and adding column names to cells
				ColumnsToAdd (templateTypeNode) ;
				//Formatting added data in cells
				_workSheet.get_Range ("A1","B1").EntireRow.Font.Bold= true ;
				_workSheet.get_Range ("A1","B1").EntireRow.Font.Color = Color.DarkRed.ToArgb() ;
				_workSheet.get_Range ("A1","B1").EntireRow.Interior.ColorIndex = 35 ;
				ValidationDataWorkSheet.get_Range ("A1", missing).AddComment (MetadataConfigName) ;
				//Freezing panes
				excelWin = (Excel.Window)(excelApp.ActiveWindow) ;
				excelWin.SplitRow = 1 ;
				excelWin.FreezePanes = true ;
				//Saving the workbook
				excelApp.Visible = false ;
				excelApp.UserControl = false ;
				if ( File.Exists(excelPhysicalFilePath) )
					File.Delete(excelPhysicalFilePath) ;
				_workBook.SaveAs(excelPhysicalFilePath,Excel.XlFileFormat.xlWorkbookNormal,null,null,false,false,Excel.XlSaveAsAccessMode.xlExclusive,false,false,null,null,null) ;

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dragonempAuthor Commented:
the error is come from this line:
_workBook.SaveAs(excelPhysicalFilePath,Excel.XlFileFormat.xlWorkbookNormal,null,null,false,false,Excel.XlSaveAsAccessMode.xlExclusive,false,false,null,null,null) ;

and if i use _workBook.SaveCopyAs(); it works.... this could be a work around for save potion, however, the _workBook.Open() has same issue.

so I'm running out of ideas, can somebody point me to right direction what could be wrong? this has to be some permission issue but I just don't see which one.
Sorry if I am barking up the wrong tree, but does you code work if the files doesn;t already exist.  But fail if you try and delete it first before saving?
The ConflictResolution you could try to set to:
xlLocalSessionChanges The local user's changes are always accepted
dragonempAuthor Commented:
no, it's not related to file existance at all, no matter file exist or not(and it's almost impossibly for the file to exist because our naming system) it works on xp/server 2003, it works as windows form app on server 2008, only time it doesn't work is when it runs from windows service on server 2008 - no matter file exist or not.
dragonempAuthor Commented:
called microsoft, its dev support said server side office automation is not recommended and it can and will stop working at any time or after any service pack/os upgrade, they suggest me to use open xml. So that'll be my solution.

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Windows Server 2008

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