The important part of the error (see screenshot) seems to be "Microsoft Excel cannot access the file", but I've checked security is lax, and that I can open it using Excel normally, so it must mean the service can't open it. TM1 Excel Service is running as Local System and has been restarted a few times.
I'm using Windows 7, Excel 2010 (but the document is 97-2003 format), TM1 9.5.1
Error from the service log is:
2010-09-27 14:11:24,744 [6] ERROR Applix.TM1.ExcelApp.ExcelApplication - Could Not Get Region Specific (html folder) Info :
System.Runtime.InteropServices.COMException (0x800A03EC): Exception from HRESULT: 0x800A03EC
at Microsoft.Office.Interop.Excel.WorkbookClass.SaveAs(Object Filename, Object FileFormat, Object Password, Object WriteResPassword, Object ReadOnlyRecommended, Object CreateBackup, XlSaveAsAccessMode AccessMode, Object ConflictResolution, Object AddToMru, Object TextCodepage, Object TextVisualLayout, Object Local)
at Applix.TM1.ExcelApp.ExcelApplication.GetSeriesFormulaRegionInfo()
2010-09-27 14:11:24,760 [6] ERROR Applix.TM1.ExcelApp.ExcelApplication - Excel could not open Xls file:
System.Runtime.InteropServices.COMException (0x800A03EC): Microsoft Excel cannot access the file 'C:\inetpub\wwwroot\TM1WebEx\ExcelSheet\41373378350312.xls'. There are several possible reasons:
• The file name or path does not exist.
• The file is being used by another program.
• The workbook you are trying to save has the same name as a currently open workbook.
at Microsoft.Office.Interop.Excel.Workbooks.Open(String Filename, Object UpdateLinks, Object ReadOnly, Object Format, Object Password, Object WriteResPassword, Object IgnoreReadOnlyRecommended, Object Origin, Object Delimiter, Object Editable, Object Notify, Object Converter, Object AddToMru, Object Local, Object CorruptLoad)
at Applix.TM1.ExcelApp.ExcelApplication.OpenFile()