There are a couple of things that can keep the installation from working.
1) Our download server is sensitive to time. Make sure that you check your computer’s time, time zone, and if you are using a 12 hour clock, the AM/PM setting. When Windows is first installed on a computer it defaults to Pacific Time Zone. Make sure that it was changed to your local time zone. The clock needs to be set to your accurate local time within 15 minutes for our download server to work. Also, check to see if you are in daylight savings time. If so, should you be?
2) During installation, when you get to the window that asks you which parts of CasaTunes you wish to install, make sure that if the Web Services box is checked you also check the Multi-room Music Server service box.

UPDATE 11/4/09, The installation program now automatically checks your computer’s clock. If it is not correct, the installation program will warn you and ask you if you want to correct it yourself, manually, of if you wish to let CasaTunes installation program correct the computer’s clock. If you let CasaTunes correct the clock, the installation will complete correctly.