Mod Error Codes (`EB1ModError`)

This document summarizes the error codes and their causes when mod inspection (compatibility check) fails.

Definition location

Source/BlueModManager/ModSystem/B1Mod.h

Fatal error

When a Fatal error (ConfigError) occurs, the mod is blocked from Manifest saving and activation.

1.Error code list

2.Detailed descriptions

ConfigError

Cause: The mod's base configuration file cannot be loaded.

Trigger	Details
`mod_manifest.json` load/parse failure	Manifest file is corrupted or does not exist
Mod name and project name mismatch	Name in manifest differs from `.uplugin` file name
`.uplugin` file load/parse failure	Plugin descriptor is corrupted or does not exist

PakFileNotFound / UcasFileNotFound / UtocFileNotFound

Cause: Mod package file structure validation failed.

PakMountError / PakUnMountError

Cause: Pak file mount/unmount runtime failure.

Error	Details
`PakMountError`	`FPakPlatformFile::Mount()` call failed — pak file is corrupted or locked by another process
`PakUnMountError`	`FPakPlatformFile::Unmount()` call failed — already unmounted or references remain

DataPatchError

Cause: An error occurred while processing the mod's JSON data patch.

Scenario	Details
Source JSON not found	Cannot find the original data (StructTag-based) to patch
Named source JSON not found	Cannot find the specified named data source
Invalid JSON value	Patch descriptor contains an invalid JSON value
Patch descriptor load failure	Failed to load `FModPatchDescriptor`
Patch application error	Patch commands (Add/Remove/Replace, etc.) failed to apply to target data
Patch result deserialization failure	Failed to convert patched JSON to struct

ShaderCompatibilityError

Cause: Shaders included in the mod are incompatible with the current game build.

AssetCompatibilityError

Cause: Mod assets are incompatible with the current game build.

Scenario	Details
Asset Hash JSON missing	Contains MPC assets but hash file is missing
MPC GUID mismatch	`MaterialParameterCollection` `StateId` differs from the game
MPC path invalid/load failure	Asset hash JSON contains an invalid MPC path
Material structure hash mismatch	Material parameter structure has changed (e.g. game update)
Material path invalid/load failure	Material asset does not exist
MFI hash mismatch	`MaterialFunctionInstance` structure has changed
MFI path invalid/load failure	MFI asset does not exist
DA exists as pak asset	DataAsset is packaged as a pak asset instead of JSON
AnimMontage Notify class load failure	Notify class referenced by montage does not exist
AnimMontage Notify property mismatch	Notify class properties differ from the game (added/removed)

LuaScriptError

Cause: Lua script validation failed for the mod.

Scenario	Details
`.lua`/`.luapak` mixed usage	Both formats used simultaneously in one mod
Static analysis (luacheck) execution failure	Error occurred while running the analysis tool
Analysis result file missing	Analysis output file was not generated
Analysis result parse failure	Output JSON file has an invalid format
Lua diagnostic error detected	Static analysis found error-level diagnostic results

- OldModKitVersion

Cause: The mod was built with an outdated ModKit version.

Scenario	Details
ModKit changelist below minimum	The second digit (changelist) of the mod version is below the minimum requirement (`11246`)

note

This check only applies to UE 5.6+ builds.

3.Mod states (EB1ModState)

State	Description
`Active`	Activated and applied to the game
`Inspecting`	Compatibility check in progress
`Unreachable`	Mod directory is inaccessible
`Broken`	Structure is corrupted
`RuntimeError`	Deactivated due to inspection failure
`AddedInGame`	Mod added in-game