0 byte recorded files

[ribbon]

Hey folks,

after years and hundreds of hours of flawless live recording with reaper, I recently experienced a massive issue

After ~3 hours of recording time (see specs below) I hit stop. Beach ball turned for a few seconds, as usual, then I ended up with a „Error while trying to save project“ message. Reaper created wav-Files for all of the tracks, but obviously no data was being saved: all files were 0 byte in size.
I tried to reimport them in another reaper session, without success. I checked the drive itself and it seemed to work properly. Then I unmounted the drive and did not reconnect it to this day, so nothing gets overwritten in case the data was there.

recording specs:

~3h of recording time, no errors whatsoever during recording, waveforms updated regularly
~90 mono tracks, 48kHz
external sync to LTC, no errors

system specs:

macbook pro 13“ retina 10,2, 2012, 2,5GHz i5, 8GB RAM
OS X 10.10.1
Reaper 4.76/64
interface: RME HDSPe MADI FX via Sonnett Echo Express
recording onto Toshiba 2TB USB3 drive, ~70% free space

Did anybody experience anything similar?

Any hints on how to proceed?

Thank you very much!

Cheers