If you are having trouble with a Workflow deployed in IIS with Windows Server AppFabric, the event log can be a wonderful tool to help diagnose problems.
Look for errors from the AppFabric Services, IIS. .NET Runtime, ASP.NET etc. Here is an example where some of my code was throwing an unhandled exception
Note: This will add additional load to your server so be careful about doing this in production environments.
If you enable the AppFabic Analytic and Debug logs you can get a ton of information on what is happening.
While troubleshooting this is a great tool