[c#] Interop type cannot be embedded

I am creating a web application on the .NET 4.0 framework (beta2) in C#.

When I try to use a assembly called "ActiveHomeScriptLib", I get the following error:

Interop type 'ActiveHomeScriptLib.ActiveHomeClass' cannot be embedded. Use the applicable interface instead.

When I change the framework to version 3.5, I don't have any errors.

What is an Interop Type and why does this only occur when I use the 4.0 framework?

Like Jan It took me a while to get it .. =S So for anyone else who's blinded with frustration.

• Right click the offending assembly that you added in the solution explorer under your project References. (In my case WIA)
• Click properties.
• And there should be the option there for Embed Interop Assembly.
• Set it to False

In most cases, this error is the result of code which tries to instantiate a COM object. For example, here is a piece of code starting up Excel:

Excel.ApplicationClass xlapp = new Excel.ApplicationClass();

Typically, in .NET 4 you just need to remove the 'Class' suffix and compile the code:

Excel.Application xlapp = new Excel.Application();

An MSDN explanation is here.

Expanding on Jon's correct answer.

The problem here is that your are combining the new "Embed Interop Types" (or NoPIA) feature with use of a class type. The "Embed Interop Types" feature works by essentially statically linking in all of the types from a PIA (Primary Interop Assembly) into the referencing assembly removing the overhead of deploying it.

This feature works great for most types in a PIA but it does have restrictions. One of them is that you cannot embed classes (it's a servicing issue). Misha has a detailed blog article on why this is not allowed

• http://blogs.msdn.com/mshneer/archive/2009/12/07/interop-type-xxx-cannot-be-embedded-use-the-applicable-interface-instead.aspx

Got the solution

Go to references right click the desired dll you will get option "Embed Interop Types" to "False" or "True".

Visual Studio 2017 version 15.8 made it possible to use the PackageReferencesyntax to reference NuGet packages in Visual Studio Extensibility (VSIX) projects. This makes it much simpler to reason about NuGet packages and opens the door for having a complete meta package containing the entire VSSDK.

Installing below NuGet package will solve the EmbedInteropTypes Issue.

Install-Package Microsoft.VisualStudio.SDK.EmbedInteropTypes

http://digital.ni.com/public.nsf/allkb/4EA929B78B5718238625789D0071F307

This error occurs because the default value is true for the Embed Interop Types property of the TestStand API Interop assembly referenced in the new project. To resolve this error, change the value of the Embed Interop Types property to False by following these steps: Select the TestStand Interop Assembly reference in the references section of your project in the Solution Explorer. Find the Embed Interop Types property in the Property Browser, and change the value to False

I ran into this issue when pulling down a TFS project to my local machine. Allegedly, it was working fine on the guy's machine who wrote it. I simply changed this...

WshShellClass shellClass = new WshShellClass();

To this...

WshShell shellClass = new WshShell();

Now, it is working like a champ!

I had same problem in VB.NET 2013 with Office 2007, and this solved it:

VS 2013 VB.NET Project > Props > Refs > Microsoft Word 12.0 Object Lib > Embed Interop Types: change True to False

Here's where to set the Embed Interop in Visual Studio 2012