I had the same problem and solved it by checking my mysql database. In var/www/fop2/lib/dblib.php i turned debug=true.
So i was able to see the SQL statment. Because in my (hand made) database the "private" column was empty and not filled with "no", so in my case the SQL returned no data.
The other time i got such an error, because i forgot to update the table to 2.1 structur. So half of the colums were no present.