problem with mastery challenge in maths

[steffffff]

i have tryed this in Opera, Chrome Newest version and an old version of firefox all with the same result, im on linux mint 17,1. everything works fine i can do individual maths subject exercises but if i try the mastery challenge i get this http://imgur.com/tNhO9zX all the buttons and links are broken and return nothing exept the close cross.
hope this was the right place to put this.

Stefan Thorpe