Not sure if the issue is caused by greenwall or swatter. The error only comes up when Swatter is enabled (lib of auctioneer) so Im think it is a swatter issue but posting here just in case

Date: 2018-09-10 13:25:31
ID: 1
Error occured in: Global
Count: 1
Message: ..\AddOns\GreenWall\Config.lua line 137:
bad argument #1 to 'gsub' (string expected, got nil)
Debug:
[C]: gsub()
GreenWall\Config.lua:137: substitute()
GreenWall\Config.lua:218: load()
GreenWall\GreenWall.lua:463: GreenWall_OnEvent()
[string ":OnEvent"]:1:
[string ":OnEvent"]:1
Locals:
(*temporary) = nil
(*temporary) = "%$(%a)"
(*temporary) = defined @interface\AddOns\GreenWall\Config.lua:137
(*temporary) = "string expected, got nil"

AddOns:
Swatter, v7.7.6095 (SwimmingSeadragon)
WowheadLooter, v80000
AngryAssignments, vv1.11.1
AngryKeystones, v
AngryWorldQuests, v
AucAdvanced, v7.7.6112 (SwimmingSeadragon)
AucFilterBasic, v7.7.6081 (SwimmingSeadragon)
AucStatHistogram, v7.7.6083 (SwimmingSeadragon)
AucStatiLevel, v7.7.6087 (SwimmingSeadragon)
AucStatPurchased, v7.7.6084 (SwimmingSeadragon)
AucStatSimple, v7.7.6085 (SwimmingSeadragon)
AucStatStdDev, v7.7.6086 (SwimmingSeadragon)
AucUtilFixAH, v7.7.6088 (SwimmingSeadragon)
BeanCounter, v7.7.6110 (SwimmingSeadragon)
DBMCore, v8.0.6
DBMDefaultSkin, v
DBMStatusBarTimers, v
DefsWhisperSound, v80000.1
Enchantrix, v7.7.6104 (SwimmingSeadragon)
GatherMate2, v1.43.4
GreenWall, v1.9.8
GTFO, v4.46.5
HandyNotes, vv1.5.3
HandyNotesBattleForAzerothTreasures, v1
InFlightLoad, v8.0.003
Informant, v7.7.6092 (SwimmingSeadragon)
InstancePortals, v19
MinimapRangeExtender, vv1
NPCScan, v8.0.1.12
Pawn, v2.2.28
PetTracker, v8.0.6
PetTrackerBreeds, v8.0.6
PetTrackerConfig, v8.0.6
PetTrackerJournal, v8.0.6
PetTrackerSwitcher, v8.0.6
PetTrackerUpgrades, v8.0.6
QEDungeonTips, v4.5.0
Rarity, v1.0 (r678-release)
RarityOptions, v
Recount, vv8.0.1b
Simulationcraft, v1.10.6
SlideBar, v7.7.6093 (SwimmingSeadragon)
Stubby, v7.7.6094 (SwimmingSeadragon)
TomTom, vv80001-1.0.2
BlizRuntimeLib_enUS v8.0.1.80000
(ck=57c)