In the past several days I've seen quite a few WSPR signals that don't decode because they are mis-timed. This happens when one's computer clock is off by more than a few seconds, and it can be prevented by using an internet time service.

The best of these -- by far, in my opinion -- is one called "Meinberg NTP." It's free, and step-by-step instructions for downloading and setting it up in Windows are available at http://www.satsignal.eu/ntp/setup.html . It works well on all recent versions of Windows, including Vista and Windows 7.

Highly recommended!

-- 73, Joe, K1JT