Cannot Enable Media Sharing

I am running Windows Vista Ultimate x64. I jump through the normal hoops,
but after I enable sharing and set all the settings, it shows that media
sharing is disabled. I found that "Windows Media Player Network Sharing
Service" is not running. WHen I start it, it starts and stopps immediately,
and the folowing event is logged in the System log:

Log Name: System
Source: Microsoft-Windows-WMPNSS-Service
Date: 4/30/2007 1:16:06 AM
Event ID: 14332
Task Category: None
Level: Error
Keywords: Classic
User: N/A
Computer: MediaPC.exampledomain.com
Description:
Service 'WMPNetworkSvc' did not start correctly because
CoCreateInstance(CLSID_UPnPDeviceFinder) encountered error '0x8002801d'.
Verify that the UPnPHost service is running and that the UPnPHost component
of Windows is installed properly.


After enabling Media Sharing, if I open Media Player and select LIBRARY->
MEDIA SHARING, it displays a dialog box saying "Media sharing is currently
disabled, either because the sharing service is not running or your firewall
settings have changed. To restart sharing, you must first confirm your
sharing settings."

I have enabled all WMP sharing-related firewall rules, and when
investigating the service, I found what I explained above.

PLEASE HELP!