saving *.xls files but troubles with opening with MS Excel

[Mimo]

Hi
I create a *.xls file and save it by
workbook.SaveAs
("testfile",Excel.XlFileFormat.xlWorkbookNormal,Type.Missin
g,Type.Missing,Type.Missing,Type.Missing,Excel.XlSaveAsAcce
ssMode.xlExclusive,Type.Missing,Type.Missing,Type.Missing,T
ype.Missing);
Everuthing is ok until I try to open the file by double-
click on it but my application is not closed. Then
Microsoft Excel runs but stops without showing the file.
Other way if I start Microsoft Excel separately and open
the file by menu: File -> Open... there is no problem even
my application is still running.
If I first stop my application there are no problems with
opening.
How could I make out with this unpleasant detail?