Thank you for talking slowly Kdyer, I get it now. So I want the value data to be Lotus notes so I changed the code to this

code
------------------------------------------------------------
If ReadValue("HKEY_LOCAL_MACHINE\SOFTWARE\Clients\Mail\Lotus Notes","")=""
$RC=WriteValue("HKEY_LOCAL_MACHINE\SOFTWARE\Clients\Mail\Lotus Notes","Lotus Notes","REG_SZ")
EndIf
------------------------------------------------------------------

and I get "script error : error in parameter(s) !.