With 3.1 (I'm guessing) Blizzard no longer gives itemRarity for all items, thus the error log below gets printed.  I think the fix is to add a check for (itemRarity == nil) before line 105 in core.lua

Do you have an error log of what happened?
Date: 2009-05-17 15:28:18
ID: 1
Error occured in: Global
Count: 1
Message: ..\AddOns\ItemLevelDKP\core.lua line 105:
   attempt to compare number with nil
Debug:
   [C]: ?
   ItemLevelDKP\core.lua:105 ilvlDKP()
   ItemLevelDKP\core.lua:84
      ItemLevelDKP\core.lua:79
   [C]: ?
   [C]: SetHyperlink()
   ..\FrameXML\ItemRef.lua:96
      ..\FrameXML\ItemRef.lua:2
   (tail call): ?
   ...ace\AddOns\Blizzard_CombatLog\Blizzard_CombatLog.lua:3603
      ...ace\AddOns\Blizzard_CombatLog\Blizzard_CombatLog.lua:3547
   (tail call): ?
   (tail call): ?
   ..\FrameXML\ChatFrame.lua:2588
      ..\FrameXML\ChatFrame.lua:2587
   [C]: ?
   [C]: ?
   [C]: ChatFrame_OnHyperlinkShow()
   [string "*:OnHyperlinkClick"]:1:
      [string "*:OnHyperlinkClick"]:1
   [C]: ?
AddOns:
  Swatter, v5.4.4157 (WallabyII)
  AHsearch, v3.1
  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
  Auditor2, v4.0
  Babylonian, v5.1.DEV.130
  Bartender4, v4.3.3
  BetterInbox, v
  BetterOutbox, v
  BigWigs, v2.0
  BindingsReminder, v0.8-20400
  Broker2FuBar, v1.0
  BrokerAuditor, v1.0
  BrokerChannelWatch, v2.1
  BulkBuy, v
  Chatter, v1.0
  Chinchilla, vv2.0.6
  ClearFont2, v2.6
  Clique, vwowi:revision
  Coconuts, v2.6.162
  Configator, v5.1.DEV.130
  DBMCore, v
  DBMLDB, v
  DebugLib, v5.1.DEV.130
  Decursive, v2.4.0.3
  DoubleWide, v
  ENStats, v2.9
  EnhancedTradeSkillUI, v30100-1
  FriendsFacts, v
  FuBar, v
  FuBarDurabilityFu, v2.11
  FuBarEmoteFu2, v0.1.5
  FuBarPerformanceFu, v2.0.0
  FuBarPitchFu, v1.0
  FuBarSpeedFu, v3.0.$Revision: 1 $
  FuBarswitcherFu, v20003-1
  FuBarVolumeFu, v2.0.$Revision: 55081 $
  GatherMate, vv1.18
  GatherMateSharing, v1.3
  GFWLinkerator, v3.1
  GoldenTicket, v1.0.13
  GoodTarget, v1.0
  GuildCheck, vv2.23
  HideLooted, vv1.2.0
  IHML, v2.3
  Informant, v5.4.4157 (WallabyII)
  InstanceMaps, v
  ItemLevelDKP, v
  LibRock10, v
  LittleWigs, v3.0.0
  LoggerHead, v3.1.0.95
  MalygosStacks, v1.1
  Mapster, v1.2.2
  MiniPet, v4.5.139
  MorgBid2, v3.82
  MorgDKP2, v3.89
  Omen, v3.0.7
  OmniCC, v2.5.2
  OmniCCOptions, v
  OneBag, v2.0.$Revision: 79491 $
  OneBank3, vv3.3.4
  OneRing, v2.0.$Revision: 55081 $
  OneView, v2.0.$Revision: 55081 $
  OptiTaunt, v0.89
  Outfitter, v4.7.2
  PallyPower, vv3.1.13-release
  Quartz, v1.0
  QuartzInterrupt, v1.0
  QuartzMirror, v1.0
  QuartzPlayer, v1.0
  QuartzRange, v1.0
  QuartzTimer, v1.0
  QuartzTradeskill, v1.0
  QuestItemBar, v0.5
  RaidBuffStatus, v3.99
  RecipeBook, v
  sct, v6.2
  SCTCooldowns, v0.7
  Stubby, v5.4.4157 (WallabyII)
  SwindlerPreventer, v3.1.1
  Talented, v2.2
  tekKompare, v3.0.3.5
  TinyTip, v0.3-Beta
  TinyTipOptions, v
  tomQuest2, v128
  TradeTabs, v
  TrainWhistle, v
  XPerl, v3.0.3b
  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
  (ck=c33)

Please provide any additional information below.