How create a multi-select Option Set in MS CRM 2011

Microsoft Dynamics CRM doesn’t support multi-select option sets out of the box, but due to som trickey work with JavaScript we can handle this event.
Just have a look on following steps:

Step 1: Create a new OptionSet field. I have used the name "sports".

Step 2: Create a new Multi-Select Text field. I have used the name "serviceinterest_value".

Step 3: Create a new Web Resource (Java Script file) I have used the name "multiselectoptionset".

Step 4: Add the following script in that JS file:

// var_new_optionset >>  Provide schema-name for Option Set field
// var_new_optionsetvalue >> Provide schema-name for field which will store the multi selected values for Option Set
// OS >> Provide Option Set field object
// OSV >> Provide text field object which will store the multi selected values for Option Set
//Method to convert an optionset to multi select Option Set
function ConvertToMultiSelect(var_new_optionset, var_new_optionsetvalue, OS, OSV)
{
if( OS != null && OSV != null )
{
  OS.style.display = "none";
  Xrm.Page.getControl(var_new_optionsetvalue).setVisible(false);
  // Create a DIV container
  var addDiv = document.createElement("<div style='overflow-y:auto; height:80px; border:1px #6699cc solid; background-color:#ffffff;' />");
  OS.parentNode.appendChild(addDiv);
  // Initialise checkbox controls
  for( var i = 1; i < OS.options.length; i++ )
  {
    var pOption = OS.options[i];
    if( !IsChecked( pOption.text , OS, OSV) )
      var addInput = document.createElement("<input type='checkbox' style='border:none; width:25px; align:left;' />" );
    else
      var addInput = document.createElement("<input type='checkbox' checked='checked' style='border:none; width:25px; align:left;' />" );
    var addLabel = document.createElement( "<label />");
    addLabel.innerText = pOption.text;
    var addBr = document.createElement( "<br/>"); //it's a 'br' flag
    OS.nextSibling.appendChild(addInput);
    OS.nextSibling.appendChild(addLabel);
    OS.nextSibling.appendChild(addBr);
  }
}
}

///////Supported functions
  // Check if it is selected
  function IsChecked( pText , OS, OSV)
  {
    if(OSV.value != "")
    {
      var OSVT = OSV.value.split(";");
      for( var i = 0; i < OSVT.length; i++ )
      {
        if( OSVT[i] == pText )
          return true;
      }
    }
    return false;
  }
  // var_new_optionsetvalue >> Provide schema-name for field which will store the multi selected values for Option Set
  // OS >> Provide Option Set field object
  // Save the selected text, this field can also be used in Advanced Find
  function OnSave(OS, var_new_optionsetvalue)
  {
    var getInput = OS.nextSibling.getElementsByTagName("input");
    var result = '';
    for( var i = 0; i < getInput.length; i++ )
    {
      if( getInput[i].checked)
      {
        result += getInput[i].nextSibling.innerText + ";";
      }
    }
    //save value
    control = Xrm.Page.getControl(var_new_optionsetvalue);
    attribute = control.getAttribute();
    attribute.setValue(result);
  }

Step 5: Add "ConvertToMultiSelect()" method on Form OnLoad event:

Step 6: Add "OnSave()" method on Form OnSave event:

Step 7: Publish the entity and enjoy........