The demo site is located at URL http://drupal7quizdemo.dev.knackforge.com/, demo users accounts are below,

HTTP Authentication, username & password - knackforge

Drupal test user accounts,

Username Password
demo1 demo1
demo2 demo2
demo3 demo3

To avoid security threat the site offers only a limited access to test users. The site will reset itself for every one hour to prevent any misuse by test users. It is recommended to create a new user account to avoid messing up with other test users. 

Also the site has been protected by HTTP Authentication, username & password for the same is knackforge.

If you experience any bug with quiz or demo site, please do report it at drupal.org quiz issue queue. For profession support and development service pertaining to quiz see our services section.