Thesis 1.8.4 and Q&A plugin - error

I instald plugin Q&A on site with thisis, but it dosn't work correctly (no css from thesis).

When I try customize like KimerlyL suggest in this post i have a error:

Fatal error: Class 'qa_loops' not found in /wp-content/themes/thesis_184/archive-question.php on line 8

How can I sovle this?