Did you contact the system administrator, like the message said?
Please elaborate greatly on your situation and hardware configuration. All we know at this point is that there's some sort of network that you cannot log in to. We don't even know what version of OS X you're running, what kind of Macintosh you're using, what "network" it is, or anything about your situation at all.
Extremely vague problem descriptions can only get you equally vague answers in return. Please elaborate and help us help you. Any additional information you think would help us diagnose your problem would be appreciated.
From the information you've provided, my only guess is that you're typing your username and password incorrectly. Try typing your username and password again, but slowly and accurately.