To me, the problem looks like you're sending "datetime('now')"
as a string, rather than a value.
My thought is to find a way to grab the current date/time and send it to your database as a date/time value, or find a way to use SQLite's built-in (DATETIME('NOW'))
parameter
Check out the anwsers at this SO.com question - they might lead you in the right direction.
Hopefully this helps!