修改AD的用户的密码出错,哎

    private void ChangeUserPassword (string commonName, string oldPassword, string newPassword)

{
            try
       {
                    DirectoryEntry de=new DirectoryEntry("LDAP://DC=***,DC=***","ADUser","ADPassword",AuthenticationTypes.Secure);
                    DirectorySearcher deSearch = new DirectorySearcher(de);
                    deSearch.Filter = "(&(&(objectCategory=person)(objectClass=user))(cn=" + commonName + "))"; 
                    deSearch.SearchScope =SearchScope.Subtree;
                    SearchResult result = deSearch.FindOne();              
                    DirectoryEntry oUser= new DirectoryEntry(result.Path);
             oUser.Invoke("ChangePassword", new Object[]{oldPassword, newPassword});
                     oUser.CommitChanges();
                     oUser.Close();
                 }
            catch(Exception ex)
            {
                        //.
                    }
        }

在oUser.Invoke("ChangePassword", new Object[]{oldPassword, newPassword});
处出错:
System.Reflection.TargetInvocationException: 调用的目标发生了异常。 ---> System.Runtime.InteropServices.COMException (0x8007202F): 出现一个约束冲突。