krazyT you dont have a static IP, which looks like it is the root of the problem here. In other words you have several different IPs and when searching for some of your different IP address it came up with several different members. When you are trying to take the quiz your IP address at that time just so happens to be the same as someone who has already taking it, therefore barring you from being able to take the quiz.
Hmmmm it reckons i have already taken the quiz. Either i have taken it and been brain washed nd am suffering from severe memory loss, or something else has happened and i havent taken it.