Build Error: Invalid Build.cs – Attempted to Load Module Outside of Plugins Folder

What It Means & How to Fix It in UE5

🧠 Why You’re Seeing This Error

This error usually shows up when you’re working with a plugin module, but its .Build.cs file is located somewhere outside the plugin’s folder, or the file structure doesn’t follow Unreal’s expected plugin layout.

UE5 expects all plugin modules to live inside:

Plugins/YourPlugin/Source/YourModule/YourModule.Build.cs

If you move the .Build.cs file or misplace your source folder, Unreal won’t treat it as a plugin module — and it throws this error.

💥 Example Error Message

Invalid Build.cs: Attempted to load module 'MyPluginModule' outside of Plugins folder

🛠️ What Usually Causes This

❌ The `.Build.cs` File Is Not Inside a Plugin’s `Plugins/` Folder

// Bad file location:
Source/MyPluginModule/MyPluginModule.Build.cs // ❌ This is a project module, not a plugin module

❌ You Meant to Build a Plugin, But Put It in the Main Source Tree

// ❌ Unreal expects plugin modules under: Plugins/YourPlugin/Source/

❌ The Plugin Folder Exists, but Your Module’s Not Inside It

// ❌ Wrong:
Plugins/MyPlugin/MyPluginModule/...

// ✅ Correct:
Plugins/MyPlugin/Source/MyPluginModule/MyPluginModule.Build.cs

✅ How to Fix It – Step-by-Step

✔️ 1. Move Your Module Into the Plugin’s `/Source/` Folder

Your folder layout should look like this:

Plugins/
└── MyPlugin/
    ├── MyPlugin.uplugin
    └── Source/
        └── MyPluginModule/
            ├── MyPluginModule.Build.cs
            ├── Public/
            └── Private/

Unreal uses this structure to recognize it as a plugin module.

✔️ 2. Make Sure the `.Build.cs` File Matches the Module Folder

Your MyPluginModule.Build.cs file must sit in:

Plugins/MyPlugin/Source/MyPluginModule/

And the class inside must match the filename:

public class MyPluginModule : ModuleRules
{
    public MyPluginModule(ReadOnlyTargetRules Target) : base(Target)
    {
        Type = ModuleType.Runtime;

        PublicDependencyModuleNames.AddRange(new string[]
        {
            "Core",
            "CoreUObject",
            "Engine"
        });
    }
}

✔️ 3. Clean and Regenerate Project Files

Once the structure is correct:

// Do this:
- Delete Intermediate/ and Binaries/ folders (optional)
- Right-click your .uproject
- Select "Generate Visual Studio project files"
- Reopen the solution and build

✅ Summary: How to Fix “Invalid Build.cs: Attempted to Load Module Outside of Plugins Folder” in UE5

Cause	Fix
Plugin module placed in wrong directory	Move module to `Plugins/YourPlugin/Source/YourModule/`
`.Build.cs` file not following layout rules	Ensure it matches the folder and file naming convention
Unreal not recognizing it as a plugin	Regenerate project files after correcting structure

UE5 Compilation Errors