Firstly, you can find here for the document guide on how to configure the plugin:http://designwall.com/guide/dw-question-answer-plugin/
If you still face there issue, you can send me username & password of your site (via private answer) for further checking.
I have helped you resolve this issue, you can check your site now.
This issue come from the shortcode that you have used in the ask question page.
[ dwqa-submit-question-form ]
I have helped you replace with the following code:
Please login or Register to submit your answer