Not Able To Enable Xp_cmdshell Using DMO

Hi,
I am using DMO + VBScript to enable the xp_cmdshell feature in SQL Server 2005 Express.
But I get error "Item cannot be found in the collection corrosponding to the requested name or ordinal".
Here is the script which I am using:

Dim excmd: Set excmd = CreateObject("ADODB.Command")
Set excmd.ActiveConnection = connx ' This was created earlier using sa login and connected to master database

excmd.CommandType = 4
excmd.CommandText = "sys.sp_configure"
excmd.Parameters.Refresh
excmd.Parameters(1).Value = "show advanced options"
excmd.Parameters(2).Value = 1
excmd.Parameters(3).Value = Null
excmd.Execute () ' This line failes
If (Err.Number <> 0) Then
LogText "Unable to execute stored procedure. " & Err.Number & " " & Err.Description
Exit Sub
End If

excmd.CommandText = "RECONFIGURE WITH OVERRIDE"
excmd.Parameters.Refresh
excmd.Execute ()
If (Err.Number <> 0) Then
LogText "Unable to Refresh. " & Err.Number & " " & Err.Description
Exit Sub
End If

excmd.CommandText = "sys.sp_configure"
excmd.Parameters.Refresh
excmd.Parameters(1).Value = "xp_cmdshell"
excmd.Parameters(2).Value = 1
excmd.Parameters(3).Value = Null
excmd.Execute ()

If (Err.Number <> 0) Then
LogText "Unable to execute sp xp_cmdshell. " & Err.Number & " " & Err.Description
Exit Sub
End If

excmd.CommandText = "RECONFIGURE"
excmd.Parameters.Refresh
excmd.Execute ()
If (Err.Number <> 0) Then
LogText "Unable to Refresh after running sp. " & Err.Number & " " & Err.Description
Exit Sub
End If

Can some body provide a clue to me !!!

Thanks in advance
Amit