if in a form there is a activeDropDownList that has error the css class "red" is not applied. i had a look at form.css and tried to change
div.yiiForm input.error, div.yiiForm textarea.error { background-color: #ffc9ca; border: 1px solid red; }
to
div.yiiForm input.error, div.yiiForm textarea.error, div.yiiForm select.error, { background-color: #ffc9ca; border: 1px solid red; }
but without success.