We'll say one thing for our friends in Redmond, they might not always be on the ball but they do recovery quickly. Not even 48 hours after we reported the problem of missing guide data for ATSC channels that no longer have an NTSC counterparts, Microsoft came up with a interim fix that should restore guide data to all those pre-TV Pack Windows Media Center users. As we suspected, the issue had something to do with the old analog channel requirement and the root source of the guide data -- you didn't think Microsoft hand coded all that information did you? Evidently one of the sources of data used for both NTSC and ASTC channels dried up, post analog shutoff, and it caught the eHome team off guard. The good news is that all should be restored when your HTPC requests new data and if your like us -- you know the impatient type -- then a quick visit to "Tasks --> Settings --> TV --> Guide --> Get Latest Guide Listings" should do the trick. The full response from Redmond after the break.
Statement from Microsoft
As reported, some Windows Media Center users experienced guide data missing for certain channels in the Windows Media Center Electronic Program Guide in Windows Vista. The channels were for a limited number of analog transmissions that were recently shut-off by local broadcasters. We are currently rolling out a solution, and expect the problem to be resolved by end-of-day today. Microsoft sincerely apologizes to those who were inconvenienced.
Additional Background
This issue affected Windows Vista users since the process for obtaining guide data was updated for the TV Pack release and subsequent releases including the Windows 7 beta. In Windows Vista, guide data was pulled from two sources – one being FCC data, and a third-party company that provided analog broadcasting info such as channel line-ups and start/end times. Microsoft then mapped both sets of data together to populate the guide. When Windows Media center first launched, both analog tuners and HD tuners were a requirement, so utilizing analog data was part of the mapping process to deliver guide info.
People started seeing their channel guide show up with "no data available" when the third party company we work with stopped providing guide data for analog channels that have been switched off - data that was needed. They are now resuming the delivery of the necessary info, which solves the problem.

iPhone 3.0 beta firmware FAQ