@mphielipp are you really using VS 2005??? Your anaconda is clearly 64-bit, hence you need to select x64 target in VS. Which nuget pythonnet package did you install? There are many versions of them.

What .NET runtime are you targetting?

What do these commands show?

where python
python --version

VS 2015
C:\Users<ny user>\AppData\Local\Continuum\Anaconda3\python.exe
Python 3.5.2 :: Anaconda 4.3.1 (64-bit)

.NET Framework 4.5.2

pythonnet_py35_dotnet 2.3.0

I see the issue, nuget does not switch automatically the version of package (x86 and x64) depending on the architecture:

https://stackoverflow.com/questions/7769580/how-should-i-create-or-upload-a-32-bit-and-64-bit-nuget-package

@denfromufa looks like you arrived to the same solution we did. We got it fixed by manually updating the dll reference to the 64bit version. I don't know how other libraries deal w this though, dllexport and nunit may have some solution for this.

@denfromufa i would like to confirm my understanding on this issue.
Do you mean that currently, the System.BadImageFormatException error still have not been solve if we downloaded Pythonnet from NuGet ?

I don't think this is something we can easily solve in code. We could, however, provide different NuGet packages for all relevant arch/python version combinations.

@filmor this should be possible with the new .NET Core nuget packages. They even support different target platforms.

That would still not solve the issue of different Python versions, would it?

@filmor , no, it would not. Python versions issue, IMHO, should either be solved by having separate NuGet package names per python version (e.g pythonnet36 instead of pythonnet), or by having all versions in a single package.

@lostmsu can you provide references for the new nuget package specs of platform definitions?

@denfromufa , I can't find a tutorial, but this is what I am talking about: https://docs.microsoft.com/en-us/dotnet/core/rid-catalog

This has been solved with the introduction of clr_loader for Python and Runtime.PythonDLL for .NET side.