fwiw - I never use file sharing but rather use the network connection available from the Finder.
Command -K >choose Browse>choose the computer you want to connect to>enter name and password.
Don't connect as a guest but rather as admin using the appropriate user and password for the machine.
U R In.
The only reasons I can think of why you can't connect using share is that afp (apple file sharing protocol) hasn't for some reason started up.
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