Thanks!
Well, this is the message that I have received in the Debug Windows:
Funci�n llamada: OnGetScriptMenu
Funci�n llamada: OnEvent_MenuClicked
Error: Ra�z no v�lida en la clave del registro "HKEY_CURRENT_USER\Software\Microsoft\MSNMessenger\PerPassportSettings\2864120175\Sounds\MSNMSGR_NewSMSMessage\Enabled"..
L�nea: 29. C�digo: -2147024894.
La funci�n OnEvent_MenuClicked devolvi� un error. C�digo: -2147352567
Sorry, the text is in spanish because I have the software in my language. If you need help for translate it, contact with me.
Please, help me!

Thanks!
Hi!
I'm happy, because I have solved the problem. I explain to you what I have done.
The entry in the registry of Windows
"HKEY_CURRENT_USER\Software\Microsoft\MSNMessenger\PerPassportSettings\2864120175\Sounds\MSNMSGR_NewSMSMessage"
not appears in my computer. I think this is because I have Windows Live Messenger in Spanish and then, some options are diferent. So, I created a new entry in the Registry with the same parameters that the others that I have find in "Sounds".
Now, Mute 1.2 funtions perfectly.
Thanks!!