I have found 2 answers leading to this error being displayed, instead of the "answer contents".
"Notice: Undefined index: content in ...cut... qa-include/qa-theme-base.php on line 1844"
Example of problem here (scroll down)
Both these answers were created by anonymous users. After doing some research, the database column content in table qa_posts, is set to NULL for these 2 answers. I suspect these could be spam users, since the IP:s seem located in China and Romania.
1. Suggestion: In case content is null, nothing should be printed as answer.
2. Question: How can these kinds of comments be stopped in the first place? (except the obvious solution, to not accept anonymous posts ;-) )