I've been searching around for days but can't find the solution.. I know this is a core bug and have found two solutions on http://drupal.org but both of them don't work for multi check box validation on my site (It works for single check box and multi radio buttons though).
These are what I have found:
My problem is that it's not outputting the error classes only for multi check box even after using those methods above. Any idea how to fix this?