CRM 2011: BLOCKED SCRIPT set email to (partylist)

Hello all,

With JScript, i´m trying to change the "to" in an email activity to fill it with 1 contact; however i´m not getting any luck,,,

This is what i have so far:

var acontacts = Xrm.Page.getAttribute("to");

var pcontact = new Array();

pcontact[0] = new Object;

   pcontact[0].id = new_contact;

   pcontact[0].name = "Name of the contact";

   pcontact[0].entitytype= "contact";

  pcontact.ParticipationTypeMask =1;

   acontacts.setValue(pcontact);

In new_contact i have the guid of the contact.

This is running onload.

What i´m i missing?

Can anyone help?

Thanks.