If your computer runs Windows XP or Vista, and you're accessing a similar "server" running Windows XP or Vista, with Simple File Sharing / Password Protect Sharing Disabled, you're going to depend upon the status of the Guest account on the server. Occasionally, you'll see a familiar error
File not accessible. You might not have permission to use this network resource. Contact the administratior of this server to find out if you have access permissions. Access is denied.Your first reaction will be to check the status of the Guest account. When you find that Guest is enabled, and with all security components properly setup, you're going to wonder
OK, now what?
The next thing that you need to do is examine the Sharing Properties of the file or folder in question. It's possible that you'll find that it now needs to be permissioned to "Everyone", and that's despite the fact that you know that you permissioned the parent folder to "Everyone", long ago.
By default, a new file or folder is owned by the account used for setting it up. If you're logged in to your server using a Full access account (equivalent to "Administrator" under Advanced File Sharing / Password Protected Sharing Enabled), that new file or folder won't be permissioned to "Everyone", but to the account that you're logged into. When you try to access the server from the network, and using the Guest account, the file or folders setup without permissions to "Everyone" won't be accessible to Guest, and you'll see the above error (or one similar).
So, besides the security benefit provided by using a limited access account, on a server with SFS / PPS disabled, you'll need to use a limited access account for setting up any files or folders that you'll be sharing. Unless you intend to manually check permissions for every new file or folder, that is.
Be consistent, and balance your file sharing / permissions setup. With just one computer running Simple File Sharing / Password Protected Sharing disabled, you'll be better off running all computers that way. And, always run under a limited access (non administrator) account on every computer, except when installing software or tweaking the system configuration.