What steps will reproduce the problem?
1. Search for several auctions using any filter
2. Sort by Seller
3. Search again for something else
4. Can't reproduce 100% of the time, but eventually the error shown bellow will pop.

What is the expected output? What do you see instead?

Should be sorting by Seller in Ascending or Descending order. Instead, it gives the error and does nothing. I can still sort with another column however.

What version of the product are you using?

1.1

Do you have an error log of what happened?

Date: 2008-11-22 23:24:57
ID: 52
Error occured in: Global
Count: 1
Message: ..\AddOns\BaudAuction\BaudAuction.lua line 568:
   attempt to compare nil with string
Debug:
   (tail call): ?
   [C]: ?
   BaudAuction\BaudAuction.lua:568
      BaudAuction\BaudAuction.lua:564
   [C]: sort()
   BaudAuction\BaudAuction.lua:564 BaudAuctionSortBrowseList()
   BaudAuction\BaudAuction.lua:373
      BaudAuction\BaudAuction.lua:298
AddOns:
  Swatter, v5.1.3715 (SnaggleTooth)
  WowheadLooter, v30015
  agExtras, v09-19-07
  agUnitFrames, v2008-08-06
  Align, v
  ArkInventory, v3.02
  Automaton, v1.3.5
  Babylonian, v5.1.DEV.130
  Bartender4, v4.2.1
  BaudAuction, v1.1
  BindPad, v1.9.0
  BonusScanner, v4.1
  ButtonFacade, v0.1Alpha
  ButtonFacadeLiteFlat, v3.0.2
  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
  CartographerProfessions, v2.0
  CartographerWaypoints, v2.0
  CartographerZoneInfo, v2.0
  Configator, v5.1.DEV.160
  CooldownButtons, v2.1.15
  DoubleWide, v
  DropJunk, v0.1
  EasyMail, v
  ElkBuffBars, v2.2.2-135
  EnhancedFlightMap, v2.0.8
  EnhancedStackSplit, v3
  Gatherer, v3.1.8
  IgorsMassAuction, v2.7.2 - Anasz
  MacroTalk, v
  MinimapTarget, vv1.1
  Omen, v3.0.3
  Outfitter, v4.3.1
  QuestHelper, v0.70
  simpleMinimap, v30000-3
  Skillet, v
  SlashToggleErrors, v1.1
  SlideBar, v3.1.8 (<%codename%>)
  Titan, v4.0.2.30000 (Revision 25)
  TitanAmmo, v4.0.2.30000
  TitanBag, v4.0.2.30000
  TitanClock, v4.0.2.30000
  TitanCoords, v4.0.2.30000
  TitanGoldTracker, v4.0.2.30000
  TitanItemBonuses, v4.0.2.30000
  TitanLootType, v4.0.2.30000
  TitanPerformance, v4.0.2.30000
  TitanRegen, v4.0.2.30000
  TitanRepair, v4.0.2.30000
  TitanVolume, v4.0.2.30000
  TitanXP, v4.0.2.30000
  TomTom, v176
  UrbinRange, v30003.1
  WOWEconPriceMod, v
  WowLua, v24
  XLoot, v0.9
  (ck=673)

Please provide any additional information below.

The following code modification seems to fix the issue:

Replace the table.sort block at line 563 with this:

  table.sort(BrowseDisplay, function(a, b)
    local sort_a = tostring(SearchResults[a][Sort])
    local sort_b = tostring(SearchResults[b][Sort])
    if(sort_a == sort_b)then
      return(a < b);
    elseif not SortReverse then
      return(sort_a < sort_b);
    else
      return(sort_a > sort_b);
    end
  end);