How much disk space do you have left ?

To check this:
telnet boulder.earthnet.net
                Connected to boulder.earthnet.net.
                Escape character is '^]'.
 
 
                SunOS UNIX (boulder.earthnet.net)
 
        login:  
        Password: 
 
        Earthnet %1>quota -v

If you are over your quota...

contact Unix Support to have your quota increased
or delete unnecessary mail/files from the server

Remember you could have files in your home, ftp and mail areas.