Interop type cannot be embedded

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.

.NET 4.0 allows primary interop assemblies (or rather, the bits of it that you need) to be embedded into your assembly so that you don't need to deploy them alongside your application.

For whatever reason, this assembly can't be embedded - but it sounds like that's not a problem for you. Just open the Properties tab for the assembly in Visual Studio 2010 and set "Embed Interop Types" to "False".

EDIT: See also Michael Gustus's answer, removing the Class suffix from the types you're using.