CRM 2011 RU12 Multi Select doesnt work since update

We are using a multi-select function in CRM 2011, it was working fine till the december update/RU12 was applied now it throws a error saying [undefined], it seems to be failing on the 2nd line here, can anyone advise how to fix this please? thanks

  // Create a DIV container
  var addDiv = document.createElement("<div style='overflow-y:auto; height:60px; border:1px #6699cc solid; background-color:#ffffff;' />");
  PL.parentNode.appendChild(addDiv);

Pete