rm ~/Library/Preferences/.GlobalPreferences.plist
Back story: When connecting to my local file server, I entered the IP address in the Connect to... dialog, and clicked Connect. When the login window popped up, I clicked on the Options button and entered some (apparently) bad settings and saved. Im my case, I turned off 'Clear text passwords' and enabled SSH. Normally, if this doesn't work, the Finder will tell you. In my case, it didn't, and it saved those prefs.
Result: I couldn't log into that server at all from the Finder, whether it be via AppleTalk or SMB. The same server worked fine from other accounts on the system. After lots of preference-juggling, I stumbled across this invisible file that made the difference.

