I resolved the problem, but unfortunately had to do a clean install of Vista to do so.
I've been running Ultimate as an upgrade from Home Premium. Unfortunately, when I tried an upgrade install, it let me reinstall Ultimate as an upgrade without harming my programs or data, but when it came time to validate it, the validation process of Vista treated it like a clean install. That meant that my upgrade product ID didn't work. Calling their validation number, they said that I had couldn't use an upgrade license for validation with them either. At that point I of course tried to do an upgrade install back to Home Premium, but the installer didn't allow that.
After two days of struggling to get it to work, I gave up and did a reinstall of Home Premium, wiping all of my programs out, but keeping my data intact under Windows.old. Then I still had to call their validation number to validate the OEM Home Premium license I had and confirm it was only used on one computer. Only then could I upgrade back to Ultimate and start the process of reinstalling my apps.
The pain is also installing all of the codecs, tools and reghacks I had to reachieve some semblance of the perfection I had at the beginning of the week. So far so good, but it will take me months to get around to reinstalling all my SW and finding all my product keys. Not very pleased with M$ right now, to say the least.
Now, however, I'm worried about accidently replicating the this ehmsas error unintentionally, and would like to find a better fix or at least a cause. I now have commercial skip working again and pretty much only have my EPG and codec hacks in place. One plugin I'm afraid of reinstalling is the Internet Radio app with all of the Swedish channels as posted here: http://www.tystpc.nu/forum/viewtopic.php?t=559
We used it a lot before, but it wasn't always stable and each station appeared as a plugin from within MCE. And I'm warry of overloading the MCE aggregator.
Still, from a clean install, I can say the MCE experience is a lot different. Tuning my channels in FireDTV only took about 20 minutes, whereas before it would take 90-120 minutes. Restoring the MCE screen down (from full screen), it now presents itself in wide screen mode instead of 4:3 as before, which is nice. Overall, it just seems more stable than before, although with two tuners I still occasionally get the error saying I can only record one show at a time.
Will be watching this thread/site for a solution to this issue and hope to avoid it or be able to better resolve it.