Just after logging in, with the message being displayed, hith Ctrl+Alt+Del to bring up the task manager. Then click File | New Task, and type in shutdown -a. This will cancel the pending shutdown request, and can be run as many times as needed. Then run the Microsoft fix given, and this should resolve the issue. I would also recommend running Windows Update and scanning your system with any available a/v scanner. At the very least, install this patch: Q823980/MS03-026: Buffer Overrun in RPC Interface May Allow Code Execution
http://support.microsoft.com/?kbid=823890