This indicates an attack attempt against a denial-of-service vulnerability in the shtml.exe component of Microsoft FrontPage.
The vulnerability is caused by an error when the vulnerable software handles a specially crafted URL whose name includes a standard DOS device name. It allows a remote attacker to cause a denial of service.
Microsoft FrontPage 2000 Server Extensions SR 1.1
Denial of service
Upgrade to FrontPage Server Extensions Service Release 1.2.