Helle everyone,
I’m experiencing the same problem.
I worked a couple of hours on a colorgrading, based on H264 Canon 5D MarkII videoclip.
Everything was ok. I saved the project, then restart DaVinci for some reason, and I had this message :

All my clips are black, and the rush bins, in the media pool in DaVinci, are empty ! The rush folders are ok on the harddrive.
Even in the DaVinci timeline, videos are black.
Davinci Lite 9 beta 0 0b 067
iMac MacOS C 10.7.4
3.06 Ghz Intel Core 2 DUO
8 Go 1067 Mhz DDR3
NVIDIA GeForce 9400 256 MB
I’m using Premiere Pro CS6 roundtrip (xml).