I have had 2 DirectTV HD TiVos, both model THR22-100, and both have had this same problem.
From time to time, one of the tuners is unable to pause/rewind/record live TV. If you are on that tuner, you will notice no green bar indicating that anything has been recorded. If you press pause, the tuner will pause, but you are unable to resume live TV. Pressing play, fast forward, rewind, etc. all do nothing. The only way to resume watching that tuner is to hit "Live TV" to switch tuners, and then switch back.
Attempting to record any programs on that tuner will result in a blank recording that can not be played.
Starting a recording (which will fail) and then stopping the recording seems to resolve the issue. The green bar will once again start to appear from the moment you started/stopped recording, and pause/play/rewind/fast forward all work again.
I have had this same issue on 2 TiVos.
This issue happened frequently on both devices. My last DirectTV HD TiVo had to be replaced after only a few months, as many recordings contained compression artifacts and would freeze/skip.
It appears to be a software issue as it can be resolved by a series of UI steps.
Has anyone else ran into this issue, and is there a known fix?
I also have an issue where the letterbox color (also shown as the screen background color when changing channels/tuners) keeps resetting to gray every so often.
I have to say I'm really disappointed in the lack of software updates, and frequency of bugs on both of the HD TiVos I've owned.
Would be nice if these devices backed up user data (season passes, favorites, ratings, etc) to the cloud, as it is really frustrating having to start over from scratch every time a device fails and has to be replaced.