I have learned a lot about VMC reading here but I have not found an answer to my exact issue.  Here's my system:
HP-Pavilion GN553AA-ABA m9040n
2.40 gigahertz Intel Core2 Quad Q6600
64 kilobyte primary memory cache
4096 kilobyte secondary memory cache
Windows Vista Home Premium Service Pack 1 (build 6001)
NVIDIA GeForce 8400 GS [Display adapter]
Hauppauge WinTV HVR-1800 (Model 78xxx, Combo ATSC/QAM)

I don't think it is important but I live in a hotel and work through their router and cable TV system. 

I've been using Media Center successfully (I thought) since December 2007 until a week ago.  Since then it has stopped recording individual programs (seven and counting).  It still records the series that I had scheduled, but when I pick a program from the guide to record in the future I get the message, "This program will not record, scheduling conflict."  But there is no apparent conflict.  Clicking to resolve the conflicts simply refreshes the screen. 

In reading other messages here, the recordings.xml file has gotten a lot of attention.  Thus I have delved into that rascal.  Here's what I've found (and some of this may not be important to those experienced with the file but for someone reading about this for the first time, it might be helpful).

1. Most basic is that the recordings.xml file can be opened in any word processor.  If you open it in Word I suggest turning off Spell Check before you open it. 
2. The top level section of the file is RecordingObjects.  After that is RecordingRequests.  Next is a slightly coded list of series and  individual programs you have asked Media Center to record since the program was first started. The series and individual requests are intermingled in order of "UniquePriority" identifier ranging from 0 through whatever.  I'm up to 85. 
   
3. Series requests always start with the term SeriesRecordingRequest
   
4. Series requests always end with /RecordingProgram and /SeriesRecordingRequest. 
   
5. Individual program requests always start with OneTimeRecordingRequest.
6. Individual program requests DO NOT always end with /RecordingProgram and /OneTimeRecordingRequest but they sometimes do.  
7. Every one of the individual programs I scheduled that failed to record is listed in the XML file with /RecordingProgram and /OneTimeRecordingRequest at the end of the listing.

One more thing.  I am one of the folks who has Bad Vista .  My computer "soft crashes" three times per week almost like clockwork.  I very seldom get a BSOD but things just stop working or it starts ignoring my settings.  Yeah I know I'm a whiner but after 12 crashes per month for 11 months crashing is starting to seem normal.  So far I have not had to reinstall anything because of crashing problems but I'm thinking VMC might be corrupted.  Certainly something is causing these closure tags to be put at the end of the files.  I am currently anticipating not recording a movie that is coming up next week because I'm getting the conflict message and the XML file verifies that it has the dreaded closure tags. 

So here are my questions. 

1. First of all, what do I have to do to fix this and stop the erronious conflict messages permanently? Is there such a thing as reinstalling VMC without reinstalling Vista? 
   
2. For the short term, can I delete the /RecordingProgram and /OneTimeRecordingRequest from the XML file and regain some control over that individual future recording? This has happened for every individual program for the last seven tries and eleven random events since I started using it. 
   

Have you removed KB955519? If not, do so and see what happens. There are several threads on scheduling problems, most of us have the problem with the ATI Cable Card tuner and series or two shows recording at once coming off a previous recording. I removed the KB955519 update because of scheduling and black screen problems. Others are reporting problems with Sony machines and various tuners.

Also are your running TV Pack 2008? You don't mention it in your run down. Don't know what effect that might have since I didn't install it (due to the recording format change).

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XPS420: Quad, 4 Gig, 650/1T internal, 3 eSata
Dual ATI Cable Cards (SA-800 M)
T-W W Valley (LA)
ATI Radeon HD3870 (DVI/HDMI)
3 Maxtor NAS (320/500/1T)
2 XP, 1 Macintosh X (10.4.11), HP 280N extender, Linksys DMA2100, DMA2200
Promise Ns4300 Raid 5

Hi John, thanks for writing.

I did not install TV Pack 2008 because I don't have a HiDef source at the hotel.  When I take my computer home I have over the air digital with some HiDef material, so I might look into it then. 

What is the issue with KB955519?  I have it on the computer so I assume it is installed.  Just cross checking the dates does not give me confidence that that is the problem.  I had these conflict issues sporadically prior to installing KB955519 and I have had plenty of success recording individual programs since installing it.  But just so I can try it, how do you uninstall a specific update?  Can it be reinstalled if the problems aren't fixed? 

The reason I posted my equipment was so that you would know I don' thave a Sony or an ATI card.  I've been reading about the headaches with those and my problem doesn't seem to correlate. 

Do you have any thoughts about modding the XML file to clear up the current issue?  I wanted to read more about that but I had to take a "work break."  I'll do a little more reading around. 

I'm experimenting with recording single programs.  I added an individual recording tonight for 6pm.  VMC never told me there was a conflict so I thought it would record the new program.  Instead it recorded an episode of a scheduled series.  As it happens the episode had been recorded previously but that happens a lot with that series. 

Armed with this possible new insight, I looked for conflicts with next week's programming where the conflict is indicated.  There is one - possibly.  Another series that I have scheduled has an episode airing at that same time.  VMC does not show that it will record, though.  So now the issue might be this:  why is it not telling me what the conflict is and also not sending me to the proper place to resolve the conflict? 

I want to experiment with this before deleting my recordings.xml and .bak files to see if I can home in on what the issue really is. 

If you scheduled a recording and it didn't record, go to recorded tv/scheduled/history and see if the show is listed there as not recorded. If so click on it and see what the error is.

Also on your series recording, go into setting and see if you have it set for first run or all and also see if you have any channel or one channel.

You can uninstall an update by going into Windows Update, history and then there is a link to remove installed updates. After it's removed you'll have to go in and "hide" the update or Windows will re-install it.

It doesn't sound as if you're having the problems with the update that the rest of us are having, it's more likely the setting in series recording are causing your problems.

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XPS420: Quad, 4 Gig, 650/1T internal, 3 eSata
Dual ATI Cable Cards (SA-800 M)
T-W W Valley (LA)
ATI Radeon HD3870 (DVI/HDMI)
3 Maxtor NAS (320/500/1T)
2 XP, 1 Macintosh X (10.4.11), HP 280N extender, Linksys DMA2100, DMA2200
Promise Ns4300 Raid 5

Yesterday I cleared the history list.  Today there are 7,391 items in the history list.  They are all dated today and yesterday.  The unrecorded programs are not there but all the recorded items are there along with future events that will not record because they are already recorded.  When you page through them the first 21 pages are different but then they start over to repeat.  When I sort it by title, all the entries are in there 13 times.  I guess when you enter each episode of each series plus the movies and do that 13 times, it adds up to 7,391...sort of.  One of my test recordings from last night only shows up 9 times so apparently it varies. 

I looked at each series I have set to record.  Each one is set to record on one channel only.  While I was there I looked at my recorded list and canceled two series from last summer's short series that I seem to have all the episodes of.  I also have all but the new ones from one other series so I changed that to First Run only.  That series is the one that potentially conflicted with next week's conflict that started this thread.  Making those changes eliminated a lot of the future recordings from the Scheduled list, but my conflict movie still shows a conflict that cannot be resolved. 

My computer just crashed last night so I'm not scheduled to restart it until it crashes again later this week.  I'll do a controlled restart after submitting this message and see if anything changes. 

Do you manipulate your recordings from outside VMC e.g deleting files or moving them to different drives / folders? I have seen history update itself whenever I do such an operation. I frequently delete recordings from outside VMC and then see that history has been updated to account for the deleted recordings.

I've been away from this computer for several days. 

I find VMC almost criminally hard to navigate.  If there is a way to do something outside of that program, I do.  So yes, I do all my file management using Windows Explorer.  It seems that if I move recordings to a folder inside the Recorded TV folder, then it keeps track of them.  If I move the recording to a different drive or delete it, then it forgets and will record the program again. 

I agree with the suggestion you should try uninstalling 955519.

That update definitely causes recording errors similar to your description with my system - or at least they started to appear MUCH more frequently since 955519 was installed.

In my case I used to miss a lot of recordings due to erroneous CGMS-A content protection flags so I am reluctant to remove 955519.  On the other hand, Media Center has missed several of my wife's "critical" TV shows in the past week (due to non-existent "recording conflicts").

In other words I'm in trouble if I leave 955519 installed and I'm in trouble if I remove it...

Note I am not running the TV Pack; just a fully updated Vista SP1 setup.

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STB w/R5000HD USB I/O, Gigabyte GA-P35-DS4, Quad Q6600, 4.0 GB RAM, ATI HD 3870 512MB, Ultra XVS 600W PSU, 3x SATA 500GB, 2x SATA 300GB, LG GGC-H20L, PVR-250, Toshiba 51H83 (51" HDTV), Yamaha RX-V2400 Amp, 5x Energy Speakers, SVS Sub, Harmony 880 Remote

I uninstalled the 955519 update and still had the oddball conflicts. 

I moved the recordings folder containing the recording.xml files to another hard drive and started over.  After about 90 seconds with the new .xml files, so far so good.