perchè si pianta dove è evidenziato in rosso???

codice:
<%


set conn = server.createObject("ADODB.Connection")
conn.ConnectionString = "Driver={Microsoft Access Driver (*.mdb)};DBQ=" & Server.MapPath("\mdb-database\utenti.mdb")
conn.open
conn.execute("SELECT * FROM tblDati where IdUsername = " & session("MM_Username")) 

  response.write "Benvenuto " & session("MM_Username") & "
"

  

rs.close
set rs = nothing

conn.close
set conn = nothing
%>

e l'errore è:

Microsoft OLE DB Provider for ODBC Drivers error '80040e10'

[Microsoft][ODBC Microsoft Access Driver] Too few parameters. Expected 1.

/Service/user.asp, line 51
grazie