That is because I took a look at one error you made, and completely forgot to fix (or indeed notice) the other one. I assumed the only error was the "it doesn't find the date" one, didn't even notice there was a formatting error as well.
Since I am presenting myself as a help guru, that is rather embarrassing.
You need to escape the brackets surrounding the date, or else it tries to read that as another character set.
Code:
(?P<author>[^_]+) - (?P<title>.+) \[(?P<published>[0-9]+)\]
EDIT: In case you are interested, "unbalanced parentheses" -- the parser is dumb enough that it took a look at the character set:
then saw
with no opening parenthesis anywhere in sight.