I had the same experience 3 days ago with 552 and MFC 16GB SDHC card. [Edit: Class 10]
The card was purchased recently and used only twice before, formatted after each time, the last formating being an hour before I started rolling.
First take recorded fine.
Sometime after that I started to get error bleeps and the Record light stayed on when not recording.
I still believed everything was going 'to tape', considering previous problems I had experienced with that LED freezing.
I vaguely remember hearing "next, 7" from SVEN, at some stage along the way when pressing stop.
I went on to record probably 10-15 takes, before trying to playback and being unable to do so.
I called off the session at that point as I knew something was wrong, and went to check the SD card in a computer but no computer/reader combination would see it.
A friend ran it through PhotoRec under Linux Mint and recovered 14 files.
The 1st recovered file was the first recording of the day.
The 2nd recovered file was the initial 20 seconds of the 2nd recording of the day (which should have been much longer).
The other files were from the previous 2 sessions ie some from before the last formating and some from 2 formatings ago.
Turns out I will be buying a Nomad after all.