The DNG Profile Editor don't recognize DNG Files converted from Olympus Pen E-P2 ORF files.
I have used the latest DNG converter 18.104.22.168 and the DNG files I have obtained can be open in Lightroom 3 beta. But the profile editor can't open them.
I have used the Profile editor for several Olympus cameras without any problem.
I have found a solution : I open the dng file version 5.6 with Camera raw 5.6 and I choose to save the image using and older version (4.1 for exemple).
The dng file that I obtain can then be opened with the Profile editor.
It seems that the Profile Editor must be upgraded for the new version of DNG.
In Adobe DNG Converter 5.6 you can choose to use an older format as 4.6 which is compatible with the Profile Editor.
Thanks to Vojtech Tryhuk !