Why Does My .NET 4.0 Application Throw an 'Interop Type Cannot be Embedded' Error?

Troubleshooting the ".NET 4.0 Interop Type Embedding" Error

During .NET 4.0 C# web application development, developers might encounter the frustrating "Interop type cannot be embedded" error. This occurs when your application tries to use an assembly that refuses embedding.

Interop, short for interoperability, enables .NET applications to interact with non-.NET components and libraries. Interop assemblies, such as "ActiveHomeScriptLib," bridge the gap between managed (.NET) and unmanaged code, allowing access to technologies like COM (Component Object Model).

The root cause in .NET 4.0 stems from a framework modification. While .NET 4.0 allows embedding parts of primary interop assemblies directly into the application, preventing separate deployment, some assemblies (like "ActiveHomeScriptLib") are incompatible with this feature, triggering the error.

The solution involves adjusting the project settings. In Visual Studio, navigate to the Assembly Properties and change the "Embed Interop Types" setting to "False." This disables the embedding process, resolving the conflict.

Another approach, suggested by Michael Gustus, involves type naming. Instead of using class names, try employing the corresponding interface names. This often eliminates the need for embedding the interop types.

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