In postgresql.conf, does the order of the listed parameters matter?
If you have several times the same parameter in postgresql.conf, the last value will override the previous ones.
I normally advise keeping the postgresql.conf file as short as possible to prevent confusion. See here.
My guess is that you misspelled something on the line you added. To be sure, you can look at Postgres logfiles which should tell you exactly what was wrong. (see here how to find your Postgres logfile.)