Covered in this google group thread

The problem was because of the extra div that was being added by the select2. Select2 had added new div with class select2-container form-select to wrap the select created. So the next time i loaded the function, the error was being thrown as select2 was being attached to the div element. I changed my selector...

Prefix select2 css identifier with specific tag name select:

$('select.form-select').select2();