the program won't let you move ahead until you reach certain goals. Sometimes I only have one or two I can work on, somtimes more. the others will open up as you work on the open boxes, and as you work on translations. You can also hover your curser over a greyed out box and see what lesson is required for it to open up.

I have the same problem... I have mastered all the previous lessons (including the one that is required for the the next lesson) but the boxes I still need to do remain gray for some reason :(

I also noticed that by doing some work on the translations some of the boxes open up. In fact, I missed a whole section because I suddenly "mastered" Clitics by working on a translation. Maybe it would help to spend some time on translating while you are trying to get those to open up.

I do see you have no boxes open! Well that is strange. I guess you could email them with the Feedback tab.

I had the same problem and now I have a solution. Browser works fine. Mobile or desktop. Have fun!