Several time , i've also changed the com number from 4 to one.
I've try with the arduino IDE and it's working and then shut down the PC and retry with B4R but the same error
I've found the problem.
Arduino where install via Windows store app and was install in the WindowsApp directory who required special authorization.
I've install another version of Arduino on a regular directory and it's working.
I think I should not be the only one who had this problem ;-)