WowAce

What steps will reproduce the problem?
1. Manual download/install of Grid2 from curse
2. Deleting old Grid2 folders from interface
3. Placing newly downloaded Grid2 folders in interface folder

What is the expected output? What do you see instead?
Unit frames that may not be exactly how I had them set up before, but there nonetheless; also a grid2 button/tab in the interface tab in-game and functionality of /grid2 command.
What is had instead is nothing.  No unit frames, no interface tab/button and no functionality of /grid2 command.

What Grid2 version and language of WoW are you using?
The latest version: released 8/21 for patch 4.2.  In English.

Do you have an error log of what happened?
This is what is in my error log:
Date: 2011-09-21 18:54:55
ID: 2
Error occured in: Global
Count: 1
Message: ..\AddOns\SlideBar\SlideMain.lua line 145:
   attempt to index global 'this' (a nil value)
Debug:
   [C]: ?
   SlideBar\SlideMain.lua:145:
      SlideBar\SlideMain.lua:145
AddOns:
  Swatter, v3.1.14 (<%codename%>)
  AtlasLootLoader, vv6.04.04
  Auctionator, v2.9.7
  Bartender4, v4.4.19
  FloTotemBar, v
  Grid2, vr619
  Grid2LDB, vr619
  Grid2RaidDebuffs, vr619
  MikScrollingBattleText, v5.6.108
  PitBull4, vv4.0.0-beta29
  PitBull4Aggro, vv4.0.0-beta29
  PitBull4AltPowerBar, vv4.0.0-beta29
  PitBull4Aura, vv4.0.0-beta29
  PitBull4Background, vv4.0.0-beta29
  PitBull4BlankSpace, vv4.0.0-beta29
  PitBull4Border, vv4.0.0-beta29
  PitBull4CastBar, vv4.0.0-beta29
  PitBull4CastBarLatency, vv4.0.0-beta29
  PitBull4CombatFader, vv4.0.0-beta29
  PitBull4CombatIcon, vv4.0.0-beta29
  PitBull4ComboPoints, vv4.0.0-beta29
  PitBull4HealthBar, vv4.0.0-beta29
  PitBull4HideBlizzard, vv4.0.0-beta29
  PitBull4Highlight, vv4.0.0-beta29
  PitBull4HostilityFader, vv4.0.0-beta29
  PitBull4LeaderIcon, vv4.0.0-beta29
  PitBull4LuaTexts, vv4.0.0-beta29
  PitBull4ManaSpark, vv4.0.0-beta29
  PitBull4MasterLooterIcon, vv4.0.0-beta29
  PitBull4PhaseIcon, vv4.0.0-beta29
  PitBull4Portrait, vv4.0.0-beta29
  PitBull4PowerBar, vv4.0.0-beta29
  PitBull4PvPIcon, vv4.0.0-beta29
  PitBull4QuestIcon, vv4.0.0-beta29
  PitBull4RaidTargetIcon, vv4.0.0-beta29
  PitBull4RangeFader, vv4.0.0-beta29
  PitBull4ReputationBar, vv4.0.0-beta29
  PitBull4RestIcon, vv4.0.0-beta29
  PitBull4Sounds, vv4.0.0-beta29
  PitBull4ThreatBar, vv4.0.0-beta29
  PitBull4Totems, vv4.0.0-beta29
  PitBull4VisualHeal5, vv4.0.0-beta29
  PitBull4VoiceIcon, vv4.0.0-beta29
  Recount, v
  ShockAndAwe, v6.20
  SlideBar, v3.1.14 (<%codename%>)
  BlizRuntimeLib_enUS v4.2.2.40200 <us>
  (ck=616)

Please provide any additional information below.
This is all I got.  If there's anything you think I could help with or expand upon, let me know. :]

SlideBar addon is crashing, try to disable it.  I could not find any link to this addon, so i cannot test/debug the issue (maybe is part of another addon ?).
Finally i have found the addon here:
http://zip.norganna.org/libs/SlideBar/
This addon is part of another addons like Gathered or Auctioneer:
The version installed on your computer is:  3.1.14
Last version is 3.2.4, i check this version and seems to work ok with Grid2.

Grid2 Options seems not installed too, without this part, you cannot access Grid2 configuration window.

If you are updating Grid2 from r560 or older version, old config is not compatible with new Grid2 versions, you must reset your saved variables (you will lose all your settings), a message in chat window must appears explaining how to reset saved variables.