Unit Tests pass fine if run one at a time, FileLoadException if run "All Tests in Solution"

Question

I'm trying to unit test some of my classes and having a problem where running the tests individually works fine 100% of the time, but if I run them in bulk / using the "All Tests in Solution" option every single test for one of my files fails with the error:

System.IO.FileLoadException was unhandled by user code
  Message=Could not load file or assembly 'Microsoft.Practices.Prism, Version=4.0.0.0, Culture=neutral, PublicKeyToken=null' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)
  Source=ServicesModuleTests
  FileName=Microsoft.Practices.Prism, Version=4.0.0.0, Culture=neutral, PublicKeyToken=null

I've been trying to figure out why for a long time and have tried searching online but haven't found anyone with this same problem.

Here is a quick example of my code:

RegistryService File:

public class RegistryService
{
    protected ILoggerFacadeExtended _Logger { get; set; }
    protected IConnectivityService _Connectivity { get; set; }

    [ImportingConstructor]
    public RegistryService(ILoggerFacadeExtended logger, IConnectivityService connectivity)
    {
        this._Logger = logger;
        this._Connectivity = connectivity;
    }

    public string GetRegistryPath(RegistryHive hive, string path)
    {
        string registryPath = string.Format("{0}\\{1}", GetRegistryHiveString(hive), path.Trim('\\'));
        _Logger.DebugWithFormat("Found registry path: {0}", registryPath);
        return registryPath;
    }

    private string GetRegistryHiveString(RegistryHive hive)
    {
        switch (hive)
        {
            case RegistryHive.ClassesRoot:
                return "HKEY_CLASSES_ROOT";
            case RegistryHive.CurrentConfig:
                return "HKEY_CURRENT_CONFIG";
            case RegistryHive.CurrentUser:
                return "HKEY_CURRENT_USER";
            case RegistryHive.DynData:
                return "HKEY_DYN_DATA";
            case RegistryHive.LocalMachine:
                return "HKEY_LOCAL_MACHINE";
            case RegistryHive.PerformanceData:
                return "HKEY_PERFORMANCE_DATA";
            case RegistryHive.Users:
                return "HKEY_USERS";
        }
        throw new ArgumentOutOfRangeException("hive");
    }
}

Test File:

private RegistryService CreateMockedRegistryService()
{
    return new RegistryService(MockRepository.GenerateMock<ILoggerFacadeExtended>(), MockRepository.GenerateMock<IConnectivityService>());
}

[TestMethod()]
public void GetRegistryPathTest_ClassesRoot()
{
    RegistryService target = CreateMockedRegistryService();
    RegistryHive hive = RegistryHive.ClassesRoot;
    string path = @"Something\SomethingElse\";
    string expected = @"HKEY_CLASSES_ROOT\Something\SomethingElse";
    string actual;
    actual = target.GetRegistryPath(hive, path);
    Assert.AreEqual(expected, actual);
}

[TestMethod()]
public void GetRegistryPathTest_CurrentConfig()
{
    RegistryService target = CreateMockedRegistryService();
    RegistryHive hive = RegistryHive.CurrentConfig;
    string path = @"Something\SomethingElse\";
    string expected = @"HKEY_CURRENT_CONFIG\Something\SomethingElse";
    string actual;
    actual = target.GetRegistryPath(hive, path);
    Assert.AreEqual(expected, actual);
}

I've dumbed down the code to try to show what I'm doing without taking up too much space here. I can run these one by one without issue, but receive the exception when run all together.

Answer 1

I figured it out by unloading other unit test projects and then running tests until it worked, apparently one of them was using some older prism references and those files were being included instead of the updated ones, the issue is now resolved after I removed and readded the references.