Loader exception : getter has no implementation

I'm debugging some code that loads a number of dlls from disk like so

AggregateCatalog aggregateCatalog = new AggregateCatalog();
LoadedPlugins loadedPlugins = new LoadedPlugins();

aggregateCatalog.Catalogs.Add(new DirectoryCatalog(pluginPath));

CompositionContainer compositionContainer = new CompositionContainer(aggregateCatalog);

compositionContainer.ComposeParts(loadedPlugins);

foreach (IPlugin plugin in loadedPlugins)
    if (!_plugins.ContainsKey(plugin.Title))
        _plugins.Add(plugin.Title, plugin);

There is one particular DDL that causes the following exception:

MSG: Unable to load one or more of the requested types. Retrieve the LoaderExceptions property for more information.

LOADER EXCEPTION: {"Method 'get_Title' in type 'Client.MyClass' from assembly 'Client.MyClass, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' does not have an implementation.":"Client.MyClass"}

I have checked my source and decompiled the dll to make sure and the public property Title is like so:

public String Title
{
    get { return "My Title"; }
}

I'm at a loss as to what is going wrong here?