VB.Net Visual Studio Error When Showing Form

Question

I get the following exception when showing a form:

InvalidOperationException was unhandled

Mixed mode assembly is build against version 'v2.0.50727' of the runtime and cannot be loaded in the 4.0 runtime without additional configuration information.

Dont really know why this isnt working. Any help?

Answer 1

I haven't seen the code for LoginForm. But I think you need to set an app.config flag to fall back to .NET 2.0 era bindings...

<startup useLegacyV2RuntimeActivationPolicy="true">
    <supportedRuntime version="v4.0"/>
</startup>

First, what's a mixed mode assembly? A mixed mode assembly is an assembly that contains both managed (CIL) and unmanaged (machine language) code. Consequently, they are not portable to other CPU instruction sets, just like normal C and C++ programs and libraries.

Next, why use them? The primary purpose for mixed mode assemblies is as "glue", to e.g. use a C++ library class as a base class of a managed class. This allows the managed class to extend unmanaged methods, allowing the managed code to be polymorphic with respect to existing unmanaged functions. This is extremely useful in many contexts. However, as something like this involves extending a C++ class, it requires that the compiler know all about the C++ compiler ABI (name mangling, virtual function table generation and placement, exception behavior), and thus effectively requires native code. If the base class is within a separate .dll, this will also require that the mixed mode assembly list the native .dll as a dependency, so that the native library is also loaded when the assembly is loaded.

The other thing that mixed mode assemblies support is the ability to export new C functions so that other programs can LoadLibrary() the assembly and GetProcAddress the exported C function.

Both of these capabilities require that the shared library loader for the platform support Portable Executable (PE) files, as assemblies are PE files. If the shared library loader supports PE files, then the loader can ensure that when the assembly is loaded, all listed dependent libraries are also loaded (case 1), or that native apps will be able to load the assembly as if it were a native DLL and resolve DLL entry points against it.

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