IE 8 problems with checkboxes

I’ve updated the plugin from 1.1.4 to 2.1.5 but when using Internet Explorer 8 the checkboxes don’t work. They work fine in Google Chrome.

I can’t put a link because it’s a test intranet on my laptop; is there a way to attach a screenshot?

http://ww.wp.xz.cn/extend/plugins/custom-login/