What is the problem? Is there any Lua errors?
When a mob starts to cast something, i get an error and the addon no longer functions. See copied error

Date: 2020-04-02 09:38:21
ID: 1
Error occured in: Global
Count: 2
Message: ..\AddOns\ClassicCastbars\ClassicCastbars.lua line 99:
attempt to call field 'UnitAuraWithBuffs' (a nil value)
Debug:
ClassicCastbars\ClassicCastbars.lua:99: CheckCastModifier()
ClassicCastbars\ClassicCastbars.lua:136: StartCast()
ClassicCastbars\ClassicCastbars.lua:156: StartAllCasts()
ClassicCastbars\ClassicCastbars.lua:209:
ClassicCastbars\ClassicCastbars.lua:170
(tail call): ?
(tail call): ?
Locals:
self = {
NAME_PLATE_UNIT_REMOVED = defined @interface\AddOns\ClassicCastbars\ClassicCastbars.lua:441
StoreCast = defined @interface\AddOns\ClassicCastbars\ClassicCastbars.lua:170
CreateOrUpdateSecureFocusButton = defined @interface\AddOns\ClassicCastbars\core/Frames.lua:425
PLAYER_ENTERING_WORLD = defined @interface\AddOns\ClassicCastbars\ClassicCastbars.lua:323
SkinPlayerCastbar = defined @interface\AddOns\ClassicCastbars\core/Frames.lua:338
ToggleUnitEvents = defined @interface\AddOns\ClassicCastbars\ClassicCastbars.lua:291
CheckCastModifier = defined @interface\AddOns\ClassicCastbars\ClassicCastbars.lua:68
DeleteCast = defined @interface\AddOns\ClassicCastbars\ClassicCastbars.lua:213
NAME_PLATE_UNIT_ADDED = defined @interface\AddOns\ClassicCastbars\ClassicCastbars.lua:430
DisplayCastbar = defined @interface\AddOns\ClassicCastbars\core/Frames.lua:239
SetBorderShieldStyle = defined @interface\AddOns\ClassicCastbars\core/Frames.lua:76
AnchorManager =

{
}
SetFocusDisplay = defined @interface\AddOns\ClassicCastbars\core/Frames.lua:474
StartCast = defined @interface\AddOns\ClassicCastbars\ClassicCastbars.lua:128
SetCastbarFonts = defined @interface\AddOns\ClassicCastbars\core/Frames.lua:194
CreateFadeAnimationGroup = defined @interface\AddOns\ClassicCastbars\core/Frames.lua:212
SetCastbarIconAndText = defined @interface\AddOns\ClassicCastbars\core/Frames.lua:56
activeFrames = {
}
CastPushback = defined @interface\AddOns\ClassicCastbars\ClassicCastbars.lua:230
StopCast = defined @interface\AddOns\ClassicCastbars\ClassicCastbars.lua:140
GROUP_ROSTER_UPDATE = defined @interface\AddOns\ClassicCastbars\ClassicCastbars.lua:452
GetCastbarFrame = defined @interface\AddOns\ClassicCastbars\core/Frames.lua:29
SetTargetCastbarPosition = defined @interface\AddOns\ClassicCastbars\core/Frames.lua:42
PLAYER_TARGET_CHANGED = defined @interface\AddOns\ClassicCastbars\ClassicCastbars.lua:423
db = {
}
PLAYER_GUID = "Player-4372-00618E47"
ClearFocus = defined @interface\AddOns\ClassicCastbars\core/Frames.lua:457
activeTimers = {
}
ZONE_CHANGED_NEW_AREA = defined @interface\AddOns\ClassicCastbars\ClassicCastbars.lua:338
SetCastbarStatusColorsOnDisplay = defined @interface\AddOns\ClassicCastbars\core/Frames.lua:226
GROUP_JOINED = defined @interface\AddOns\ClassicCastbars\ClassicCastbars.lua:452
0 =
UNIT_AURA = defined @interface\AddOns\ClassicCastbars\ClassicCastbars.lua:408
SetLSMBorders = defined @interface\AddOns\ClassicCastbars\core/Frames.lua:169
defaultConfig = {
}
StartAllCasts = defined @interface\AddOns\ClassicCastbars\ClassicCastbars.lua:151
SetCastbarStyle = defined @interface\AddOns\ClassicCastbars\core/Frames.lua:110
HideCastbar = defined @interface\AddOns\ClassicCastbars\core/Frames.lua:275
StopAllCasts = defined @interface\AddOns\ClassicCastbars\ClassicCastbars.lua:161
GetUnitType = defined @interface\AddOns\ClassicCastbars\ClassicCastbars.lua:57
COMBAT_LOG_EVENT_UNFILTERED = defined @interface\AddOns\ClassicCastbars\ClassicCastbars.lua:486
}
unitID = "target"
cast = {
isPlayer = false
maxValue = 2.500000
timeStart = 1728735.783000
unitGUID = "Creature-0-4380-0-3-1834-000005E760"
spellID = 25292
endTime = 1728738.283000
icon = 135920
spellName = "Holy Light"
}
libCD = {
Register = defined @interface\AddOns\ZPerl\Libs\LibClassicDurations\core.lua:690
dataVersions = {
}
guidAccessTimes = {
}
GetAuraDurationByUnit = defined @interface\AddOns\ZPerl\Libs\LibClassicDurations\core.lua:665
Talent = defined @interface\AddOns\ZPerl\Libs\LibClassicDurations\core.lua:159
enableEnemyBuffTrack
AddOns:
Swatter, v8.2.6377 (SwimmingSeadragon)
Atlas, vv1.47.00.11303.00
AtlasClassicWoW, vv1.47.00.11303.00
AtlasLootClassic, vv1.4.7
AtlasLootClassicData, vv1.4.7
AtlasLootClassicDungeonsAndRaids, vv1.4.7
AucAdvanced, v8.2.6430 (SwimmingSeadragon)
AucFilterBasic, v8.2.6364 (SwimmingSeadragon)
AucStatHistogram, v8.2.6366 (SwimmingSeadragon)
AucStatiLevel, v8.2.6370 (SwimmingSeadragon)
AucStatPurchased, v8.2.6367 (SwimmingSeadragon)
AucStatSimple, v8.2.6399 (SwimmingSeadragon)
AucStatStdDev, v8.2.6369 (SwimmingSeadragon)
AucUtilFixAH, v8.2.6371 (SwimmingSeadragon)
Bartender4, v4.9.0
ClassicCastbars, vv1.3.2
ClassicCastbarsOptions, v
Coordinates, v2.1.0
DBMCore, v1.13.42
DBMDefaultSkin, v
DBMStatusBarTimers, v
Enchantrix, v8.2.6428 (SwimmingSeadragon)
EnchantrixBarker, v8.2.6469 (SwimmingSeadragon)
ExoLink, v1.0.1
ExoLinkBIS, v1.0.1
ExtendedCharacterStats, v2.2.1
GatherMate2, v1.45.5
GroupCalendar, v
HideRaidManager, v1.0
honorspy, v1.7.3
Informant, v8.2.6374 (SwimmingSeadragon)
LeatrixPlus, v1.13.56
NugEnergy, v1.13.14
OmniCC, v8.3.5
Pawn, v2.3.24
Questie, v5.10.0 0 fd3ff918
Recount, vv1.13.4a
SlideBar, v8.2.6375 (SwimmingSeadragon)
Stubby, v8.2.6376 (SwimmingSeadragon)
ThreatClassic2, v2.12
TomCats, v0.0.2
WeaponSwingTimer, v4.1.0
ZPerl, v5.9.3
ZPerlArcaneBar, v
ZPerlParty, v
ZPerlPartyPet, v
ZPerlPlayer, v
ZPerlPlayerBuffs, v
ZPerlPlayerPet, v
ZPerlRaidAdmin, v
ZPerlRaidFrames, v
ZPerlRaidHelper, v
ZPerlRaidPets, v
ZPerlTarget, v
ZPerlTargetTarget, v
BlizRuntimeLib_enUS v1.13.4.11304
(ck=656)

What steps will reproduce the problem?

Does the issue still occur when all addons except ClassicCastbars are disabled?

Any additional info? If you play on a non English client, please include your locale:

Fixed now. Seems like one of your addons is embedding a very old and outdated version of LibClassicDurations which screws it up.

Will upload the fix tomorrow.