As I entered Ulduar raid as a solo I got a pop-up error shown that I have an "Incomplete DBM installation"
I checked and I have the addon shown installed and running. I even refresh it and tried again and see the same error.

Do you have an error log of what happened?
Date: 2024-08-10 10:08:20
ID: 1
Error occured in: Global
Count: 1
Message: Interface/AddOns/Atlas_BurningCrusade/Core/Data.lua line 760:
attempt to concatenate a nil value
Debug:
[string "@Interface/AddOns/Atlas_BurningCrusade/Core/Data.lua"]:760: in main chunk
Locals:
_G =

{
UpdateOnBarHighlightMarksBySpell = defined @Interface/AddOns/Blizzard_ActionBar/Classic/ActionButton.lua:70
ERR_OUT_OF_CHI = "Not enough chi"
DH_HAVOC_CORE_ABILITY_2 = "Strong melee attack that consumes Fury. If it critical strikes, some Fury is refunded."
MultiCastActionButton6Cooldown = MultiCastActionButton6Cooldown {
}
SettingsSliderOptionsMixin = {
}
GetTrainerServiceTypeFilter = defined =[C]:-1
UNIT_NAMES_COMBATLOG_TOOLTIP = "Color unit names."
UNIT_NAMEPLATES_TYPE_TOOLTIP_3 = "This method avoids overlapping nameplates by spreading them out horizontally and vertically."
SetTrainerServiceTypeFilter = defined =[C]:-1
LE_GAME_ERR_CHAT_RAID_RESTRICTED_TRIAL = 796
SPELL_FAILED_CUSTOM_ERROR_71 = "This partygoer wants to dance with you."
LE_GAME_ERR_PET_SPELL_TARGETS_DEAD = 412
ERROR_CLUB_TICKET_COUNT_AT_MAX_COMMUNITY = "Can't create any more invite links for this group."
CompactUnitFrameProfilesGeneralOptionsFrameHealthTextDropdownButtonNormalTexture = CompactUnitFrameProfilesGeneralOptionsFrameHealthTextDropdownButtonNormalTexture {
}
MultiCastActionButton2Cooldown = MultiCastActionButton2Cooldown {
}
ERR_TRADE_EQUIPPED_BAG = "You can't trade equipped bags."
PVP_RANK_6_1 = "Corporal"
MultiBarLeftButton7 = MultiBarLeftButton7 {
}
InterfaceOptionsNamesPanelUnitNameplatesShowAll = InterfaceOptionsNamesPanelUnitNameplatesShowAll {
}
VideoOptionsFrameCategoryFrameButton17ToggleHighlightTexture = VideoOptionsFrameCategoryFrameButton17ToggleHighlightTexture {
}
MerchantItem1AltCurrencyFrameItem1Text = MerchantItem1AltCurrencyFrameItem1Text {
}
OPTION_TOOLTIP_ACTION_BUTTON_USE_KEY_DOWN = "Action button keybinds will respond on key down, rather than on key up."
BINDING_NAME_NAMEPLATES = "Show Enemy Name Plates"
INSTANCE_UNAVAILABLE_OTHER_TEMPORARILY_DISABLED = "%s cannot enter. This instance is temporarily disabled."
MultiBarBottomRightButton8Shine5 = MultiBarBottomRightButton8Shine5 {
}
MAIL_LETTER_TOOLTIP = "Click to make a permanent
copy of this letter."
UnitFrameManaBar_UnregisterDefaultEvents = defined @Interface/AddOns/Blizzard_UnitFrame/Classic/UnitFrame.lua:776
CALENDAR_RAID_RESET_DESCRIPTION = "%1$s resets at %2$s."
CHAT_CONFIG_OTHER_COMBAT = {
}
CONSOLIDATED_BUFFS_PER_ROW = 4
MoneyFrame_OnEvent = defined @Interface/AddOns/Blizzard_MoneyFrame/Classic/MoneyFrame.lua:232
BN_UNABLE_TO_RESOLVE_NAME = "Unable to whisper '%s'. Blizzard services may be unavailable."
CinematicFrameRaidBossEmoteFrame = CinematicFrameRaidBossEmoteFrame {
}
CompactRaidFrameManagerDisplayFrameHiddenModeToggleTopRight = CompactRaidFrameManagerDisplayFrameHiddenModeToggleTopRight {
}
LFGTeleport = defined =[C]:-1
LE_GAME_ERR_ONLY_ONE_QUIVER = 33
INT_SPELL_DURATION_HOURS = "%d |4hour:hrs;"
ToggleEncounterJournal = defined @Interface/AddOns/Blizzard_UIParent/Cata/UIParent.lua:559
LOSS_OF_CONTROL_DISPLAY_FEAR = "Feared"
Graphics_QualityText = Graphics_QualityText {
}
OverrideActionBarButton6Shine11 = OverrideActionBarButton6Shine11 {
}
ChatFrame4MinimizeButton = ChatFrame4MinimizeButton {
}
JoinSkirmish = defined =[C]:-1
Advanced_GraphicsAPIDropDownButtonHighlightTexture = Advanced_GraphicsAPIDropDownButtonHighlightTexture {
}
MultiBarRightButton7Shine9 = MultiBarRightButton7Shine9 {
}
BankFrameItem17SearchOverlay = BankFrameItem17SearchOverlay {
}
DMG_LCD = "DMG"
RaidGraphics_EnvironmentalDetailSlider = RaidGraphics_EnvironmentalDetailSlider {
}
Is64BitClient = defined =[C]:-1
SecureCmdItemParse = defined @Interface/AddOns/Blizzard_ChatFrameBase/Classic/ChatFrame.lua:1148
SLASH_STOPATTACK1 = "/stopattack"
MultiCastActionButton4HotKey = MultiCastActionButton4HotKey {
}
ATLAS_DDL_CONTINENT_BROKENISLES2 = "Broken Isles Raids"
CompactRaidFrameManagerDisplayFrameFilterOptionsFilterRoleTankMiddleMiddle = CompactRaidFrameManagerDisplayFrameFilterOptionsFilterRoleTankMiddleMiddle {
}
SortQuestWatches = defined =[C]:-1
ContainerFrame4I
AddOns:
Swatter, v4.4.6991 (SwimmingSeadragon)
WowheadLooter, v40400
Atlas, vv1.52.08
AtlasBattlegrounds, vv1.52.03
AtlasBurningCrusade, vv1.52.03
AtlasLootClassic, vv4.0.1
AtlasLootClassicData, vv4.0.1
AtlasLootClassicDungeonsAndRaids, vv4.0.1
AtlasLootClassicMaps, vv1.0.0
BlizRuntimeLib v4.4.0.56014(US)
(ck=146)

To Reproduce
-- Steps to reproduce the behavior:

1. Go to Ulduar as a solo.
2. Step in but not in a raid.

Screenshots

Did you try having DeadlyBossMods as the only enabled addon and everything else (especially something like ElvUI) disabled?
Yes same error showing

Which version of DeadlyBossMods are you using? r336 (guessing as this is part of the Zip file name.

Was it working in a previous version? If yes, which was the last good one? No idea

Additional context

lua error unrelated, that's a diff addon entirely called Atlas_BurningCrusade

As for the DBM popup, you may have wrath module installed but perhaps not enabled. open addons list in escape menu on login screen and make sure wrath raid modules are enabled with a golden checkbox