I am following the German and Spanish courses through English. I have come to a point in both where I am unable to move forward and am forced to repeat lessons ad infinitum. I thought at first I would only have to repeat once or twice but now even if I repeat the last lessons presented twenty times the system remains stuck. I am hoping some admin people will see this and that it will be fixed.
You never have to repeat!
Strengthen only those skills you really want to do.
This is my favourite method
Link to some background information about word and skill decay