Yahoo has updated the security level of their servers such that Fund Manager running on Windows XP is no longer able to retrieve prices from Yahoo. If you're running Fund Manager under Windows XP you can either switch to a different quote server, or update to a newer version of Windows.
More Technical Details:
Fund Manager and Internet Explorer both use the same component of Windows called WinInet to access the internet. If IE cannot access a website, then Fund Manager will not be able to either. You can see the SSL server test here. If you scroll down to the handshake simulation section and look at "IE 8 / XP" you can see it isn't working. You can also verify this issue by trying to load Yahoo Finance with IE from Windows XP, and see that isn't working either.