HELP please : 500 : Internal Server Error



Yesterday, I tried to complete the 3rd Graded Assignment of the “Simulation Neuroscience” MOOC. At first, I managed to edit my collabs but then it says, for every collab and new collab :
500 : Internal Server Error
Failed to start your server. Please contact admin.

And now : redirected you too many times.

What should I do ?

Thank you in advance for your help !