Due to the lack of space left on the CF Card, i recorded MP3 320 kbit today.
Since the situation was very stealthy, I had to keep the recorder in my pocket.
The unit ran out of power -> file has length 0 bytes, seems to be lost completely.
Wouldn't have happened with my DAT recorder ... 
its still there, just no file header was written so you'll have to open as raw file
Sorry to hear that you lost a file. Maybe with some of the other's suggestions it's retrievable. I thought I'd try and reproduce your situation and see if this problem happens all the time or maybe only some of the time. I've had it run out of power on me before but it's always saved the file before shutting down. It's always been wav files too though I think.
So back to your situation. Were you recording from the S/PDIF or one of the analog ports? You mentioned that you had it set to 320 kbit, was that 44.1 or 48k? Was the hodl switch on or off? What brand and size of CF card were you using? How much space was left and how long do you think it recorded before it shut off (you're best guess if you have no idea or at least something like "it was no longer than x because that's when I notcied it was off").
Perhaps the problem was that I used an external Battery. The recorder showing something to 1/2 of battery left, so I connected an unregulated 5 Volt Battery via Mini USB.
It was 44.1 khz 320kbit MP3. 1/8 In. I watched the unit record the first ~2-3 minutes and everything worked fine. Hold was enabled. I checked again after about 3 hours and the unit was off then. At home, i connected
the MT to my PC. The file was there but it has length 0 bytes. I tried all the checkdisk stuff from windows but it didn't change anything. The CF Card was fragmented before recording, there were some files on it,
and i deleted some of them just before the recording. I did not format the CF since I needed some of the files that i recorded previously.
I use an ExtreMemory 2GB CF Card (80x).
I'll try to reproduce the problem, but that will take some time. I think the unit might try to save the file whenever it senses the internal battery going down. I fear that in my case the external
battery was going out of power, and the MT could not detect that. I thought 2400 mAh 5 Volt (NiMH) should be sufficient for 3 hours, but maybe there is a lot of loss because the internal LI Akku is loaded from the external one or something.
I didn't check the external battery Voltage, sorry, forgot about that. Since after the 3 hours the unit was not booting with external connected, i think it was dead.
It's nice to hear that you ran out of power and it saved your .wav files. Perhaps the problem occurs only with MP3, who knows. I record WAV most of the time.
It was just a meeting, no music, so it's not such a big problem. I like to record meetings and then hear afterwards how things were going, gives me another perspective and helps me improving my skills.
its still there, just no file header was written so you'll have to open as raw file
No it's not. Its a 0 byte file. There is nothing. If it was the only file and the card was not fragmented, there might have been a chance to edit the FAT or something in order to read the card. Since MP3 is a streaming format this should work as well as reading a Wav file, even if you start from the middle.