Question : offline server ,active director

Hallo,
im a student im still learning thing about windows 2003 ,

When my server is connected to the internet , than i can open active directory users and computers with no problem but when iùm offine and i try to open active directory users and computers i get an error

naming information cannot be located for the following reason:
the server is not oprational.

.....

My quastion is this , is it normal i get this error when im offline ? and why its giving me this error ?

THank you

Answer : offline server ,active director

Is DNS is working on your server? Check it please.