What version of TellMeWhen are you using? ("The latest" is not a version)
6.1.3

Do you have an error log of what happened?
Date: 2013-03-05 16:08:04
ID: 2
Error occured in: Global
Count: ∞
Message: ...ents\Core\Conditions\Categories\PlayerAttributes.lua line 71:
   attempt to call upvalue 'GetInstanceDifficulty' (a nil value)
Debug:
   ...ents\Core\Conditions\Categories\PlayerAttributes.lua:71 GetZoneType()
   [string "Condition_INSTANCE"]:3: CheckFunction()
   ...TellMeWhen\Components\Core\Conditions\Conditions.lua:1063 Check()
   ...TellMeWhen\Components\Core\Conditions\Conditions.lua:916
      ...TellMeWhen\Components\Core\Conditions\Conditions.lua:888
   (tail call): ?
   [C]: ?
   [string "safecall Dispatcher[3]"]:9:
      [string "safecall Dispatcher[3]"]:5
   (tail call): ?
   TellMeWhen\TellMeWhen.lua:863
      TellMeWhen\TellMeWhen.lua:834
   TellMeWhen\TellMeWhen.lua:1012
      TellMeWhen\TellMeWhen.lua:987
   (tail call): ?
   ...TellMeWhen\Components\Core\Conditions\Conditions.lua:1248 Construct()
   TellMeWhen\TellMeWhen.lua:3591 Setup_Conditions()
   TellMeWhen\TellMeWhen.lua:3674
      TellMeWhen\TellMeWhen.lua:3607
   (tail call): ?
   [C]: ?
   [string "safecall Dispatcher[1]"]:9:
      [string "safecall Dispatcher[1]"]:5
   (tail call): ?
   TellMeWhen\TellMeWhen.lua:1935 Update()
   TellMeWhen\TellMeWhen.lua:3016 ?()
   ...Ons\Ace3\CallbackHandler-1.0\CallbackHandler-1.0.lua:147
      ...Ons\Ace3\CallbackHandler-1.0\CallbackHandler-1.0.lua:147
   [string "safecall Dispatcher[1]"]:4:
      [string "safecall Dispatcher[1]"]:4
   [C]: ?
   [string "safecall Dispatcher[1]"]:13: ?()
   ...Ons\Ace3\CallbackHandler-1.0\CallbackHandler-1.0.lua:92 Fire()
   Ace3\AceEvent-3.0\AceEvent-3.0.lua:120
      Ace3\AceEvent-3.0\AceEvent-3.0.lua:119

Please provide any additional information below (including any export strings if applicable; see above.)
http://www.wowpedia.org/API_GetInstanceDifficulty -
"MoP Patch 5.2.0 (2013-03-05): Removed. Use GetInstanceInfo and GetDifficultyInfo."