is a Microsoft Dr. Watson error-collector and reporting tool. It harvests information about disfunctional software and sends a report to Microsoft. It's totally harmless.
What's happening is that something is crashing just before Windows shuts down, and dwwin.exe is launched so that it can gather information for a resport. Unfortunately because Windows is shutting down dwinn.exe can't launch, and so you get the error message.
My guess is that it's associated with the nvidia driver - have you downloaded the latest version?