@Rahul, Downloaded zip file from above url. Deactivated and removed previous plugin and installed new version from above url. Manually install means installation by uploading file in wp admin? if yes I did that also. but the error consist. Also when clicking on sign up it shows pop up but the submit button name login instead of register or sign up.
Get latest version from here: https://github.com/open-wp/anspress and manually install it and then let me know.
Thank you it works. Now how to stop it from creating duplicate page titles? Look please. http://ecopsi.org/query-response/