Note that this error only occur occasionally.
(The below error post is from EU-Hellscream, trying to open cooking)

What steps will reproduce the problem?
1. Open spell book
2. Open any profession

What is the expected output? What do you see instead?
Expected is to see list of recipies, outcome is that no list or profession frame open.

What version of the product are you using?
r38beta

Do you have an error log of what happened?

Date: 2009-04-19 19:02:17
ID: 2
Error occured in: Global
Count: 1
Message: ...ace\AddOns\GnomishYellowPages\GnomishYellowPages.lua line 2653:
   table index is nil
Debug:
   [C]: ?
   ...ace\AddOns\GnomishYellowPages\GnomishYellowPages.lua:2653
      ...ace\AddOns\GnomishYellowPages\GnomishYellowPages.lua:2645
   ...ace\AddOns\GnomishYellowPages\GnomishYellowPages.lua:2818 ?()
   ...ace\AddOns\GnomishYellowPages\GnomishYellowPages.lua:1469
      ...ace\AddOns\GnomishYellowPages\GnomishYellowPages.lua:1466
   [C]: CastSpell()
   ..\FrameXML\SpellBookFrame.lua:350 SpellButton_OnClick()
   [string "*:OnClick"]:4:
      [string "*:OnClick"]:1
AddOns:
  Swatter, v5.4.4157 (WallabyII)
  WowheadLooter, v30100
  Ace2, v
  Ace3, v
  AceGUI30SharedMediaWidgets, v3.2
  ArkInventory, v3.02
  AtlasLoot, vv5.04.01
  AtlasLootFu, vv5.04.01
  AucAdvanced, v5.4.4157 (WallabyII)
  AucFilterBasic, v5.4.4157 (WallabyII)
  AucFilterOutlier, v5.4.4157.2531
  AucMatchUndercut, v5.4.4157.2531
  AucScanData, v5.4.4157 (WallabyII)
  AucStatClassic, v5.4.4157 (WallabyII)
  AucStatHistogram, v5.4.4157 (WallabyII)
  AucStatiLevel, v5.4.4157 (WallabyII)
  AucStatPurchased, v5.4.4157 (WallabyII)
  AucStatSales, v5.4.4157.2842
  AucStatSimple, v5.4.4157 (WallabyII)
  AucStatStdDev, v5.4.4157 (WallabyII)
  AucStatWOWEcon, v5.4.4157.2530
  AucUtilAHWindowControl, v5.4.4157.3311
  AucUtilAppraiser, v5.4.4157.2530
  AucUtilAskPrice, v5.4.4157.3175
  AucUtilAutoMagic, v5.4.4157.3142
  AucUtilCompactUI, v5.4.4157.2530
  AucUtilEasyBuyout, v5.4.4157.3583
  AucUtilItemSuggest, v5.4.4157.3108
  AucUtilPriceLevel, v5.4.4157.2545
  AucUtilScanButton, v5.4.4157.2530
  AucUtilScanFinish, v5.4.4157.2530
  AucUtilScanProgress, v5.4.4157.2530
  AucUtilSearchUI, v5.4.4157.3655
  AucUtilSimpleAuction, v5.4.4157.0
  AucUtilVendMarkup, v5.4.4157.2530
  Babylonian, v5.1.DEV.130
  BadBoy, v3.0.0.2
  BeanCounter, v5.4.4157 (WallabyII)
  beql, v1.0.3:3.0.3
  BrokerLunarSphere, v1.0
  Cartographer, v2.0
  CartographerBattlegrounds, v2.0
  CartographerCoordinates, v2.0
  CartographerFoglight, v2.0
  CartographerGroupColors, v2.0
  CartographerGuildPositions, v2.0
  CartographerInstanceLoot, v2.0
  CartographerInstanceMaps, v2.0
  CartographerInstanceNotes, v2.0
  CartographerLookNFeel, v2.0
  CartographerNotes, v2.0
  CartographerPOI, v2.0
  CartographerWaypoints, v2.0
  CartographerZoneInfo, v2.0
  Clique, vwowi:revision
  Configator, v5.1.DEV.130
  CurseProfiler, v
  DBMCore, v
  DebugLib, v5.1.DEV.130
  dgks, v1.99
  dgksfemale, v$Rev: 28 $
  Enchantrix, v5.4.4157 (WallabyII)
  EnchantrixBarker, v5.4.4157 (WallabyII)
  FuBar, v
  FuBarBagFu, vv1.1.5
  FuBarDungeonDiFu, v1.0.20300
  FuBarDurabilityFu, v2.11
  FuBarExperienceFu, v1.1 $Revision: 65606 $
  FuBarGroupFu, v1
  FuBarMoneyFu, vv1.2.1
  FuBarOutfitterFu, v
  FuBarPerformanceFu, v2.0.0
  FubarRecountFu, v3.0
  FuBartTracker, v0.2
  FuBaruClock, v2.1
  FuBarWintergraspFu, v1.0-release
  GnomishYellowPages, vr35
  IceHUD, v1.5.3 (Revision: 375)
  Informant, v5.4.4157 (WallabyII)
  LibBetterBlizzOptions10, v1.0
  LibRock10, v
  LibRockComm10, v
  LibRockConfig10, v
  LibRockEvent10, v
  LibRockHook10, v
  LibRockModuleCore10, v
  LibRockTimer10, v
  LibSharedMedia30, v3.0-56
  LunarSphere, v1.04
  LunarSphereExporter, v1.04
  MalygosStacks, v1.0.1
  NRT, v3
  Omen, v3.0.7
  Outfitter, v4.5.2
  PowerAuras, v2.6.0
  Prat30, v3.1.5
  Prat30HighCPUUsageModules, v
  Prat30Libraries, v
  RatingBuster, v
  Recount, v
  RecountFailBot, v
  RecountGuessedAbsorbs, v
  RecountThreat, v
  RPText, v1.0
  SexyMap, v
  SlideBar, v5.4.4157 (WallabyII)
  Stubby, v5.4.4157 (WallabyII)
  TellMeWhen, v1.1
  Thaddius, v3.0
  XPerl, v3.0.3
  XPerlArcaneBar, v
  XPerlParty, v
  XPerlPartyPet, v
  XPerlPlayer, v
  XPerlPlayerBuffs, v
  XPerlPlayerPet, v
  XPerlRaidAdmin, v
  XPerlRaidFrames, v
  XPerlRaidHelper, v
  XPerlRaidMonitor, v
  XPerlRaidPets, v
  XPerlTarget, v
  XPerlTargetTarget, v
  ZOMGBuffs, v$Revision: 58 $
  ZOMGBuffsLog, v$Revision: 58 $
  ZOMGBuffsSelfBuffs, v$Revision: 58 $
  (ck=d3f)