I have been using my newly built Media Center PC for about a week before I started getting errors from my TV Tuner card.  In my Media Center PC, I have an ATI eHome TV Wonder card with the additional FM tuner.  When a show was scheduled to start to record, I would get a little popup message from the system tray telling me that the recording failed.  After I saw that message, I started up Media Center and noticed that Live TV no longer worked as well.  I would get an error message as shown below:

Initially, I would just reboot my computer and then it would work just fine again.  However, after it kept happening, that was no longer a practical solution.  I started researching the error and dug into the event viewer.  I found that when MCE tried to record a show, I would get and error in my event log:

Event Type: Error
Event Source: Media Center Receiver
Event Category: None
Event ID: 3
Date:  4/25/2005
Time:  1:04:14 PM
User:  N/A
Computer: STEVED1
Description:
TV tuner encountered an error. (0xc0040524) ATI eHomeWonder TV Tuner

For more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp.

As shown above, the error was not very descriptive.  I began searching the web and newsgroups for an answer.  Initially I thought that it was some sort of hardware conflict because of what seemed like a random nature of the error.  But after reading a thread in Google Groups  posted by other users that have had the same problem, I discovered that it was a software conflict. 

It turns out AOL's AIM instant messenger software is the cause of my problems.  I don't know exactly what AIM is doing to cause the TV Tuner to have problems but now that I have uninstalled AIM from my computer, my problem is solved.

If you are experiencing a similar error as shown above, try uninstalling AIM and most likely, your problem will be solved.  Try other AIM clients such as GAIM to replace your IM client.  GAIM works perfectly with MCE.