OS 10.8.4 Pages 4.1 (923)
The document did not appear in Pages 'Open recent' either. Nor Cmd + F / Spotlight.
I think its a problem about Auto-save... but its strange that it removes any trace of the original file.
Thanks for you support anyway. I just had to redo the work from the previous 'Time Machine' version. But I am contining to get 'problem auto-saving file' messages... I am immediatley printing to PDF to keep a draft copy of my Ph.D thesis.