Regarding the defragmenting process described by SeÃ¡n above, I would like to amplify a bit from my experience with the LVW-5045. If you defrag a file on the HDD that is longer than 2 hours, you will lose any material in that file after the 2 hour mark. This includes the ability to play, edit and record anything after that point.
The distinction here from what SeÃ¡n said is that even though the file may have been recorded with compression higher than SP (like LP or Just Fit) AND the file would normally fit on a DVD (even though it is longer than 2 hours), the damage in defrag happens at the 2 hour mark, regardless of file size.
I am not sure why this happens but I have experienced it a few times. The missing program material appears to be lost, maybe in unlinked clusters in the FAT. I have upgraded to version 203 firmware, but this probably is unrelated to firmware.