Session has disappeared upon file open


i had been working on a fairly small ardour session. it was saved and closed. i opened again and all of a sudden a blank session appears with these errors:

[ERROR]: Could not understand ardour file /MAIN/AUDIO/VALE_and_VESSEL/vv_1/Pt_I_intro.ardour
[ERROR]: Session “/MAIN/AUDIO/VALE_and_VESSEL/vv_1 (snapshot Pt_I_intro)” did not load successfully

the .ardour, .ardour.bak, .history, and .history.bak files are all there in the folder but i do not know what to do now. other files (sessions) open fine. just this one is now gone.

everything was fine. saved file. closed. opened again and it’s gone.

ardour v2.0.5 on mac os x.4.11 PPC.