Joël,
Your code uses a loop unnecessarily. You just need one line of code to remove the item. Try this:
Public Sub Effacer_etu()
Try
_listeEtu.Remove(_etudiant)
Catch ex As Exception
MsgBox(ex.Message)
End Try
End Sub
You will get the same result without the unnecessary looping.
solved How to remove the actual item in my ArrayList