The following is a description that covers the timeline of a test I did. It involved the following activities:
 
1. A scheduled recording of the movie "Dante's Peak" is attempted.
2. The recording fails.
3. I reactivate the recording from the Upcoming Recordings menu.
4. It seems to start recording again.
5. A check of recorded shows reveals that it thinks it is still recording but, in fact, there is no recording file.
6. I deleted the file (by pressing "D") and indicated to allow re-record.
7. I switched to LiveTV and tuned the movie which worked fine.
8. I pressed "R" and it began recording (which, eventually ended successfully).

THe following is an excerpt from the backend log covering the above steps (only up to the beginning of step 8 -- the conclusion of the recording isn't
included:
Code:
2011-08-24 06:42:15.486 mythbackend: Running housekeeping thread
2011-08-24 07:10:13.987 QueryBasename found no entry for 6410 @ 2011-08-24T07:10:00
2011-08-24 07:10:14.021 QueryBasename found no entry for 6410 @ 2011-08-24T07:10:00
2011-08-24 07:10:14.099 TVRec(10): Changing from None to RecordingOnly
2011-08-24 07:10:14.115 TVRec(10): HW Tuner: 10->10
2011-08-24 07:10:15.397 LFireDev(001692D3FE120000): Buffered packets 2000 (8000 KB)
2011-08-24 07:10:15.642 TVRec(10): rec->GetPathname():
'/6410_20110824071000.mpg'

============================================================================
=
2011-08-24 07:10:15.654 TFW, Error: Opening file '/6410_20110824071000.mpg'.
  eno: Permission denied (13)

NOTE: This makes it look as if it was trying to put the recording file into the root directory where it has no permissions to create files. That makes no sense -- none of my storage directories are the root directory and in the cases where it works properly it certainly doesn't store anything in the root directory.
============================================================================
=

2011-08-24 07:10:15.670 TVRec(10) Error: RingBuffer '/6410_20110824071000.mpg' not open...
2011-08-24 07:10:15.690 TVRec(10): Changing from RecordingOnly to None
2011-08-24 07:10:15.719 Finished recording Dante's Peak: channel 6410
2011-08-24 07:10:15.742 scheduler: Finished recording: Dante's Peak: channel 6410
2011-08-24 07:16:31.118 ProgramInfo(6410_20110824071000.mpg), Error:
GetPlaybackURL: '6410_20110824071000.mpg' should be local, but it can not be found.
2011-08-24 07:17:02.010 MainServer::ANN Monitor
2011-08-24 07:17:02.027 adding: MythTVFrontEnd as a client (events: 2)
2011-08-24 07:17:46.392 ProgramInfo(6410_20110824071000.mpg), Error:
GetPlaybackURL: '6410_20110824071000.mpg' should be local, but it can not be found.
2011-08-24 07:17:46.785 ProgramInfo(6410_20110824071000.mpg), Error:
GetPlaybackURL: '6410_20110824071000.mpg' should be local, but it can not be found.
2011-08-24 07:17:49.431 Error deleting
'GetPlaybackURL/UNABLE/TO/FIND/LOCAL/FILE/ON/MythTVFrontEnd/6410_20110824071
000.mpg' could not open 
   eno: No such file or directory (2)
2011-08-24 07:17:49.453 Delete Error
'GetPlaybackURL/UNABLE/TO/FIND/LOCAL/FILE/ON/MythTVFrontEnd/6410_20110824071
000.mpg'
   eno: No such file or directory (2)
2011-08-24 07:17:54.035 MainServer::ANN Playback
2011-08-24 07:17:54.045 adding: MythTVFrontEnd as a client (events: 0)
2011-08-24 07:17:54.098 TVRec(10): Changing from None to WatchingLiveTV
2011-08-24 07:17:54.135 TVRec(10): HW Tuner: 10->10
2011-08-24 07:17:54.333 LoadFromScheduler(): Error, called from backend.
2011-08-24 07:17:55.619 TVRec(10): Changing from WatchingLiveTV to None
2011-08-24 07:18:06.056 MainServer::ANN Playback
2011-08-24 07:18:06.088 adding: MythTVFrontEnd as a client (events: 0)
2011-08-24 07:18:06.125 TVRec(10): Changing from None to WatchingLiveTV
2011-08-24 07:18:06.150 TVRec(10): HW Tuner: 10->10
2011-08-24 07:18:06.342 LoadFromScheduler(): Error, called from backend.
2011-08-24 07:18:07.696 LFireDev(001692D3FE120000): Buffered packets 2000 (8000 KB)

============================================================================
==202011-08-24 07:18:08.478 Finished recording The Ranger, the Cook and a Hole in the Sky: channel 6490

NOTE: Just to clarify, this "recording" being ended is the show which was on the initial channel when I changed to LiveTV. It ended when I changed the channel.
============================================================================
===

2011-08-24 07:18:08.517 scheduler: Finished recording: The Ranger, the Cook and a Hole in the Sky: channel 6490
2011-08-24 07:18:08.582 LoadFromScheduler(): Error, called from backend.
11-08-24 07:18:08.628 Finished recording The Ranger, the Cook and a Hole in the Sky: channel 6490
2011-08-24 07:18:08.721 LFireDev(001692D3FE120000): Buffered packets 2000 (8000 KB)
2011-08-24 07:18:11.336 RecBase(10:/dev/video):
GetKeyframePositions(28,9223372036854775807,#0) out of 1
2011-08-24 07:18:11.370 RecBase(10:/dev/video):
GetKeyframePositions(28,9223372036854775807,#0) out of 1
2011-08-24 07:18:36.488 TVRec(10): HW Tuner: 10->10
2011-08-24 07:18:36.519 LoadFromScheduler(): Error, called from backend.
2011-08-24 07:18:36.576 Finished recording The Ranger, the Cook and a Hole in the Sky: channel 6490
2011-08-24 07:18:38.123 LFireDev(001692D3FE120000): Buffered packets 2000 (8000 KB)
2011-08-24 07:18:38.475 Finished recording Dante's Peak: channel 6410
2011-08-24 07:18:38.506 scheduler: Last message repeated 2 times: Finished
recording: The Ranger, the Cook and a Hole in the Sky: channel 6490
2011-08-24 07:18:38.530 scheduler: Finished recording: Dante's Peak: channel 6410
2011-08-24 07:18:38.550 LoadFromScheduler(): Error, called from backend.
2011-08-24 07:18:38.608 Finished recording Dante's Peak: channel 6410
2011-08-24 07:18:38.687 LFireDev(001692D3FE120000): Buffered packets 2000 (8000 KB)
2011-08-24 07:18:41.966 RecBase(10:/dev/video):
GetKeyframePositions(32,9223372036854775807,#0) out of 1
2011-08-24 07:18:41.999 RecBase(10:/dev/video):
GetKeyframePositions(32,9223372036854775807,#0) out of 1 Error in my_thread_global_end(): 1 threads didn't exit
2011-08-24 07:18:54.024 TVRec(10): SetLiveRecording(1)
2011-08-24 07:18:54.078 TVRec(10): SetLiveRecording() -- record
2011-08-24 07:19:39.197 TVRec(10): Changing from WatchingLiveTV to RecordingOnly Error in my_thread_global_end(): 1 threads didn't exit
2011-08-24 07:20:31.800 New DB connection, total: 4
2011-08-24 07:20:31.864 Connected to database 'mythconverg' at host:
192.168.0.235