Sorry for the long post, I want to give all the details to be clear on what's happening.
I have a Series 3 TiVo using two M-Cards from Comcast.
Several weeks ago there was a problem where I could no longer access Netflix. I've had this problem / error before with different TiVo HD in my house. I checked my network switches and router and rebooted them, just in case but found nothing wrong. When I had this problem with the TiVo HD I ended up rebooting the TiVo and that solved the Netflix problem.
After checking my network, I rebooted the S3 TiVo. When the S3 booted up it presented an error regarding the cable cards, I think the error was 161-4. It said to contact my cable provider to resolve the issue. Once that message was displayed I couldn't really do anything with the TiVo. Clicking buttons on the remote would change screens on the TiVo but after a few seconds the error would reappear on the screen, locking me out.
My wife called Comcast the next day and they tried to reset the cable cards with a "hit" or whatever it is that they do. They couldn't resolve the issue and scheduled a truck / technician to come out and resolve the issue. Comcast replaced one of the two cable cards in the TiVo (the card in the top slot, slot 2). That resolved the issue for about two weeks, although during that time I noticed tiny audio dropouts on my local ABC affiliate HD channel in both recorded programming and live TV.
After a couple weeks Netflix stopped working so I rebooted the TiVo S3 again. Again I had the same error message when the TiVo booted back up. This time I tried power cycling the TiVo. The power cycle put the S3 into a reboot loop where it would never start up properly. After fooling with that for a while I pulled the plug on the TiVo and went to bed.
The next day I found a thread here that described a problem where the TiVo would get stuck in a reboot loop when the user had a cable card installed. This person said that they could remove the cable cards and the TiVo would boot but of course they couldn't watch or record TV without the cable cards.
I decided to remove one of the cable cards, the newer one that Comcast had installed a couple weeks earlier and booted the TiVo. The TiVo booted normally. When it came up it told me there had been a change in the number of cable cards and then it warned me that I wouldn't be able to record / watch two things at once without two cable cards. I proceeded on and it worked fine but could only record one show at a time.
Later I tried moving the cable cards around in the slots so the newer card was in the bottom slot and the older card was in the top slot. This caused the TiVo to reboot and get stuck in the reboot loop again. Long story, a little bit shorter, I tried every combination of cards in the different slots and the TiVo would always work fine with one card inserted but would always get stuck in a reboot loop with more than one card inserted.
After that I contacted TiVo tech support. The rep on the phone told me that the problem was that I was using two M-Cards and that the S3 only needed one. I spent some time trying to convince him that I did need two cards in the S3 and eventually he checked with his supervisor and acknowledged that I was correct. Then he suggested I contact Comcast again and have them bring two new cable cards. That sounded reasonable so I called Comcast.
Comcast came out an hour and 1/2 late and I had to convince them that installing a cable box was not what I needed they installed two different cable cards. The TiVo worked normally again except for the audio dropouts on ABC HD, That was until today. When I came home at lunch time, I found the S3 rebooting over and over again. I ejected the top cable card and the TiVo booted normally.
So I was convinced that Comcast cable cards were the problem and not my beloved TiVo but now I don't know. Do I need to ask Comcast to come out again for a third round of cable cards? The S3 worked fine for years and now this issue keeps reoccurring. Could there be a problem with the top cable card slot on the TiVo?
My TiVo HD with a single M-Card continues to work fine, except for the occasional need to reboot it when Netflix stops working, which is rare.