In two instances I have have a number of Mac Minis and iMacs that were not connected to the Internet but a local isolated LAN have their
SMB:// shares refuse to connect, though they worked days or weeks before with no configuration changes.
After some testing I found that
CIFS:// connections still worked using the same username and password as the non working SMB connections.
Since 10.9.x uses SMB by default now I wanted to figure out what was causing the issue instead of switching to AFP or CIFS as many have suggested.