Found the problem using the simplified project. Just a dumb mistake. I had an extra instance of the WclAdapter that isn't used and it wasn't being closed out.
Line 17 in WclAdapter: protected static WclAdapter Instance = new WclAdapter();
Deleted the line, and no more error.
Edit: Shutdown is being called in the simplified project from MainWindow's closing event. My original Zip was missing that, but I updated it.