More than one export was found that matches the constraint exception with MEF ImportMany

[admin]

I'm trying to debug an assembly import issue on a WPF app that uses MEF to load some plugins and looking for ideas to solve this particular exception:

<blockquote>
More than one export was found that matches the constraint:<br>
ContractName MarkPad.Contracts.ISpellingService<br>
RequiredTypeIdentity MarkPad.Contracts.ISpellingService
</blockquote>

There is only one assembly that references the plugin of concerndirectly as part of an autofac registration of it (code snippet at the very end).

[ImportingConstructor]
public SpellCheckPlugin(
    IPluginSettingsProvider settingsProvider,
    ISpellingService spellingService,
    ISpellCheckProviderFactory spellCheckProviderFactory)

There is only 1 implementation of

ISpellingService

[Export(typeof(ISpellingService))]
public class SpellingService : ISpellingService

This is an open source <a href="https://github.com/Code52/DownmarkerWPF" rel="nofollow">Code52 project on github</a>.

The plugin import is:

[ImportMany]
IEnumerable<IPlugin> plugins;

<strong>What I've tried so far:</strong>

<ol>
<li><a href="http://marlongrech.wordpress.com/2010/05/03/mef-deploymentcatalog-and-reference-assemblies/" rel="nofollow">This</a> and <a href="http://geekswithblogs.net/abhijeetp/archive/2011/10/30/mef-101---part-2.aspx" rel="nofollow">this blog</a> post make reference to using

[ImportMany(AllowRecomposition = true)]

but that also doesn't seem to help. </li>
<li>Other discussions I found mention setting the 'Copy Local' to false, but because it's actually used in registration code that's not an option, as it doesn't end up in the output folder.</li>
</ol>

<strong>Any ideas?</strong>

The registration code referencing the plug-in

builder.RegisterType<SpellingService>().As<ISpellingService>()
    .SingleInstance()
    .OnActivating(args =>
{
    var settingsService = args.Context.Resolve<ISettingsProvider>();
    var settings = settingsService.GetSettings<SpellCheckPlugin.SpellCheckPluginSettings>();
    args.Instance.SetLanguage(settings.Language);
})