I just read this thread and perhaps missing something but I'd suggest the following:
whichever .xml files were in the project folder check if any have additional lines that represent content rather than just the initial default learning object line.
If for instance data.xml has content by preview.xml doesn't then you can try copying data.xml and renaming as preview.xml
If data.xml has truncated e.g. has content but has become corrupted and doesn't end with </learningObject> you could try comparing the xml with a working project and try to finish the xml for the page where it became truncated and then finish with </learningObject> and see if that restores access. Obviously only worth the effort if there is a lot of work still in the xml before it became corrupted.
I've been working on a tutorial about avoiding lost work and what the different (but rare) causes are but just haven't had a chance to finish it yet.
HTH
Ron