Error words

Hello, I'm a Server Enginner, and I need to make 3 patters error messages. If you know any other error messages, please tell me. I'm not good at English.

Target device is NewWork device. The messages shows up when you login to NewWork device, and failed to login.

Pattern1: situation is you just faile to login to the NetWork device. (The login attempt failed) (unable to login, something wrong) (login failed)

Patter2: You are already logined to NW device, but failed change to root user. (Administrative Permission denied.) (Administrator authorization is required.) (Unable to change root mode.)

Pattern3:failed backup(backup script didn't work well) (config backup is failed) (config backup is unsuccessful)

Please give me some advices, I want make smart error messages.