DNS Zone Editor and Sub Domain issue

Hello Dear, I have 2 Issue and I cannot fix it. First issue is that when I try to make sub domain I get an error message and I have attach you the error message and the list of DNS, the issue is only with this name when I want create a sub domain with this name (login.xxx.xx) it shows this error in the image. Second Issue is that when I create a new DNS Cname with only this name (login.xxx.xx) it is not working when I want to link it with another host it is not working how can you help me how to solve this issue??