# IL2CPP error: BadImageFormatException: Could not resolve field token 0x04000001

- **ID:** `unity/il2cpp-bad-image-format`
- **Domain:** unity
- **Category:** build_error
- **Error Code:** `0x04000001`
- **Verification:** ai_generated
- **Fix Rate:** 87%

## Root Cause

A managed assembly contains a reference to a field that does not exist in the compiled IL, often due to partial recompilation or mismatched assembly versions.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| Unity 2022.3 | active | — | — |
| Unity 2023.2 | active | — | — |
| Unity 6000.0 | active | — | — |

## Workarounds

1. **Perform a full rebuild: delete the Library and Temp folders, then recompile the project from scratch.** (85% success)
   ```
   Perform a full rebuild: delete the Library and Temp folders, then recompile the project from scratch.
   ```
2. **Ensure all custom DLLs are compiled with the same .NET version and API compatibility level as the project.** (90% success)
   ```
   Ensure all custom DLLs are compiled with the same .NET version and API compatibility level as the project.
   ```

## Dead Ends

- **** — The issue is in the managed assemblies, not in generated data; a full rebuild is needed. (50% fail)
- **** — Code stripping removes unused code but does not affect broken metadata references. (80% fail)