TypeLoadException was unhandled in C#

Question

I'm fairly new to C#, and am having a problem when loading a library into my program. Im trying to run this example in visual studio, but I am getting an error:

TypeLoadException was unhandled. Can't load type SVM.Problem from assembly SVM, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null.

This is what my code looks like:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using SVM;

namespace SVM
{
class Program
{
    static void Main(string[] args)
    {
        //First, read in the training data.
        Problem train = Problem.Read("a1a.train");
        Problem test = Problem.Read("a1a.test");

        //For this example (and indeed, many scenarios), the default
        //parameters will suffice.
        Parameter parameters = new Parameter();
        double C;
        double Gamma;

        //This will do a grid optimization to find the best parameters
        //and store them in C and Gamma, outputting the entire
        //search to params.txt.
        ParameterSelection.Grid(train, parameters, "params.txt", out C, out Gamma);
        parameters.C = C;
        parameters.Gamma = Gamma;

        //Train the model using the optimal parameters.
        Model model = Training.Train(train, parameters);

        //Perform classification on the test data, putting the
        //results in results.txt.
        Prediction.Predict(test, "results.txt", model, false);
    }
}

}

I have added the dll as a reference via the solution explorer. What could be going wrong?

---

I have started a new project, added the dll as a reference, ran the project and now everything works. Very frustrating not to know what went wrong, but I suspect it had something to do with the project name and the dll name being the same. Thanks for helping!

Answer 1

EDIT: Okay, due to your answer, I've now managed to reproduce the problem without SVM. Basically, you shouldn't have two assemblies with the same name, one in a .exe and one in a .dll. Here's an example:

Library.cs:

public class Library
{
    public static void Foo()
    {
        System.Console.WriteLine("Library.Foo");
    }
}

Test.cs:

public class Test
{
    static void Main(string[] args)
    {
        Library.Foo();
    }
}

Compile:

> csc /target:library /out:Test.dll Library.cs
> csc /r:Test.dll Test.cs

Run:

> test.exe

Unhandled Exception: System.TypeLoadException: Could not load type 'Library' from
assembly 'Test, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null'.+
    at Test.Main(String[] args)

It's already loaded an assembly called Test from Test.exe... so it's not going to also look for Test.dll.

Answer 2

I wanted to add this as a comment (but not high enough rep yet) - I had this exact issue and found @JonSkeet answer really useful, between myself and a colleague we stumbled on the answer;

https://stackoverflow.com/a/13236893/692942.

Basically my project assembly which generated an EXE file was named the same as a referenced assembly I built as a class library. The combination of the EXE and DLL in the build directory cause the error to be thrown as only one assembly of that name could be loaded.