System.InvalidCastException error

try it like this

Dim oExcel As Excel.Application = CType(CreateObject("Excel.Application"), Excel.Application)

Dear Ronald,
it still doesn't work now

the reason is, you are actually trying combine 2 methods, late and early binding

it should be either

this (late binding)

       Dim oExcel As Object
       oExcel = CreateObject("Excel.Application"), Excel.Application
       Dim wbk As Object

        wbk = oExcel.Workbooks.Open(Filename:="C:\temp\test.xls", UpdateLinks:=False, ReadOnly:=False)
        With wbk.ActiveSheet
            .Range("B1").Value = "Iouri" & .Range("A1").value
            .Range("B2").Value = "Iouri" & .Range("A2").value
            .Range("B3").Value = "Iouri" & .Range("A3").value
            .PrintOut()
        End With ' wbk

etc...
or this (early binding)

  Dim oExcel As Excel.Application = New Excel.Application
  Dim objWS As New Excel.Worksheet
         
            ObjExcelWrite.Workbooks.Open(WriteFilepath)
            ObjExcelWrite.Visible = False
            objWS = ObjExcelWrite.Worksheets.Item(1)
            objWS.Cells.Clear()

etc...

sorry the last should be
  Dim ObjExcelWrite As New Excel.Application
  Dim objWS As New Excel.Worksheet
         
            ObjExcelWrite.Workbooks.Open(WriteFilepath)
            ObjExcelWrite.Visible = False
            objWS = ObjExcelWrite.Worksheets.Item(1)
            objWS.Cells.Clear()

it is still not working, the fact that my code run well yesterday, but today it doesn't work anymore, I don't know why.

Both the methods I gave should work (I tested them)

Do you have excel installed on the computer you are testing this on.
The second method can't give you an invalidcast error so what is the error you get there

Yes, you are right, even my code run well on another PC, but I don't why it doesn't work on my PC. Maybe the problem is not syntax. If I can't fix this error, I must reinstall Window

that sounds a bit drastic, maybe the excel object is just corrupt

Maybe try this...

System.Diagnostics.Process.Start("D:\PMO\VB.NET\Test\Test\bin\Test.xls")

I believe this will launch almost any type of known file...

The other thing to see is if D-Drive is mapped on the machines both the same way, and if they both have the same security privelages...

I removed office 2000 and install office 2003, with my code, another error show up
An unhandled exception of type 'System.Runtime.InteropServices.COMException' occurred in mscorlib.dll

Additional information: Member not found.

P/S:I choose MS Excel 5.0 Object Library in item Project\Add Reference\COM tab

ok, I changed MS Excel 5.0 Object Library to 11.0 and it run well now.
anyway thanks you guys alot

5.0, no wonder it didn't work, glad you got it solved :-)