Copy a project - by: Damien Gozillon

I created Default Projet or Model (Modele in French).
The problem is I cannot copy it. I have an error message (see attachement).
I put a date and charge in every task (it should'nt be necessary in a model anyway...) but I still have this message.
I tried to cha,ge the type of projet but I still have the mesage.
And I can't see where is the problem.
Can you please help me ?