Unable to connect to server.

We have a SOHO of 8 users who are all networked with a main hub using and share a DSL line. I am experiencing problems connecting to a computer we call the server, its not really a server but a fast machine. The rest of the computers can see the Server in the Computers Near Me but when you double-click on the Server to access the computer, you get a error message: “\\Server is not accessible.
The user has not been granted the requested logon type at this computer.”