Which version of Overachiever are you using?
0.45

What steps will reproduce the problem?
1. Travel to Witergrasp.
2. Open achievement UI.
3. Select suggestions tab.

Do you have an error log of what happened?
Date: 2009-08-08 18:45:13
ID: 1
Error occured in: Global
Count: 1
Message: ..\AddOns\Overachiever_Tabs\build.lua line 225:
   attempt to compare string with nil
Debug:
   (tail call): ?
   [C]: ?
   Overachiever_Tabs\build.lua:225
      Overachiever_Tabs\build.lua:199
   [C]: sort()
   Overachiever_Tabs\build.lua:267
      Overachiever_Tabs\build.lua:255
   Overachiever_Tabs\build.lua:321    Overachiever_Tabs\build.lua:313
   Overachiever_Tabs\build.lua:382 ForceUpdate()
   Overachiever_Tabs\Suggestions.lua:475
      Overachiever_Tabs\Suggestions.lua:402
   [C]: Show()
   Overachiever_Tabs\build.lua:485
      Overachiever_Tabs\build.lua:484
   [C]: Show()
   ...ns\Blizzard_AchievementUI\Blizzard_AchievementUI.lua:196 AchievementFrame_ShowSubFrame()
   Overachiever_Tabs\build.lua:417
      Overachiever_Tabs\build.lua:398

Does this problem occur when all other addons are disabled? If not, use the process of elimination and report where the addon conflict lies (including the version of the conflicting addon).
It happens with only Overachiever enabled.

Please provide any additional information below.
Using spanish language pack. WoW 3.2 release.