Malicious Code?

Hi, I am having a few problems, when I access a website - pokeheroes.com (its a website that you sign up and create an account and use the website’s various areas). I have been using the website for a number of months and with no previous problems.
I go to one of their games and click on it to play it (bearing in mind its a direct on the website game does not open up any other browsers etc.) It says that your avast software has blocked a html script inf. Now I have been in contact with some of the admins on the site and they have checked, and double checked the script for the whole site and nothing is wrong with the coding or anything else.
I have also been in contact with another users on the site and they also use avast as their anti virus software and they are having the same problem as I am. Another admin has played the game and she uses AVG anti virus soft ware and has had no problem. Is this a false positive from avast? If so can I correct it?
I have run a virus scan on my mac and nothing has shown up. In am also using the most update version of avast for mac. So I am not sure what to try. Any ideas would be much appriciated.

You can report a suspected FP here: https://support.avast.com/support/tickets/new?form=3