Hello Pierre,
Presuming that you are using Project Server authentication...
Log into PWA as Administrator, or using an account with administrator
priveledges on the project server.
Goto PWA | Admin | Manage Users and Groups.
Select the user that is having the problem and click the Modify User option.
On the modify user page select the Reset Password option and enter a new
password for the user. Click OK and then Save.
The user should be able to login using the new password and then change their
password using the option on their home page.
Does this answer your question?
Bob Segrest, PMP
Microsoft Project Blackbelt