Unfortunately when the user change the password in Windows 7 it's a nightmare to found the window handling them.
There's a command line to directly open the window and "save" the user who wants to access to an important data for a meeting. In a PowerShell run the following command line:
rundll32.exe keymgr.dll, KRShowKeyMgr
The rest is easy: deleting the account :)
Thanks to Romain to point out the problem and for the solution.