with Trac 10.4 and decent SQLite. It seems that string in SQLite (in my configuration) is stored as 'DD-MM-YYYY', while the plugin uses 'DD/MM/YYYY' format, thus SQL query doesn't find existing row -- and fails upon issuing INSERT (rather than UPDATE, which would be issued should the plugin find previous entry).
The difference in formatting of date field may be due to regionall setting (LOCALE).
I kinda fixed it by commenting out:
#date_time = now.strftime("%d/%m/%Y");
and adding above it following code:
date_time = str(now.date())
(I'm sorry it's not a real patch, I'm in hurry now >_>;; )